The psychology of web performance

First and foremost, we are human. We can’t get around it, and some things will make us anxious, frustrated, and mad. As much as we like to think we are optimists, we frequently don’t notice something until it disappoints us in some way. In this article, we will take a look at how web performance and psychology impact user satisfaction.

When things work as expected, we go on happily yet oblivious to the amount of time and money spent to produce something that we can immediately take for granted. The more oblivious we are to the mechanics of the interaction, the happier we are, and our perceptions of the tool or product are generally pretty good—the way it should be. When things are not living up to our expectations, we become agitated, frustrated, and sometimes angry. The surprising part is that there is only a few seconds or micro-seconds between satisfaction and frustration. Is this need for speed due to an ever-growing feeling of entitlement? Have we become so used to instant gratification we just can’t tolerate waiting anymore? You will be surprised to learn that neither entitlement nor low attention spans are responsible for our need for fast computer-human interactions.

The psychology behind performant websites and apps

You might think this increasing need for speed is just another aspect of our short attention spans, and you may think we feel a little entitled or spoiled because we always want more. The truth is, nothing has really changed. Research has gone on for centuries on human interaction, brain function, thought processing, and flow (we will get to this and more in a moment), and the data remains pretty conclusive; to maintain concentration and productivity, a response in under two seconds is necessary. One of the first human to computer interaction studies was conducted by Robert B. Miller in 1968 in his article titled Response time in man-computer conversational transactions.

Miller’s research supported the age-old findings that for effective communication some response is needed within two seconds of a request. A wait longer than two seconds breaks concentration and affects productivity. If the interaction were to take longer than two seconds, setting expectations about the response time frame reduced frustration, but it doesn’t do anything for the thought process. A meaningful response occurs in under two seconds otherwise a breakdown in thought process and internal and external distractions demand the attention of the user. Psychologists connect this need for fast responses with what they call “flow.”

Fast sites and apps support optimal user experience (flow)

Flow, as described by Mihaly Csikszentmihalyi in the article Flow: The psychology of optimal experience, is, “a state of concentration so focused that it amounts to absolute absorption in an activity.” Also referred to as “The zone,” flow is said to be a pleasurable and satisfying experience that brings happiness to the person experiencing it. Flow does not come from leisure activities but instead comes from times of intense concentration on a difficult task.

That difficult task may be optimizing a Trello board, conducting academic research, learning how to fix a washing machine, finding the right gear for your softball team, or matching the right accessories with an outfit for a first date. Whatever the task at hand may be, the more focus we can retain while completing the task the more pleasurable the experience, so if the user is racing through your well thought out site or application with wait times under two seconds, their user experience is optimal. The user is accomplishing their goals, and having achieved flow, she finishes with pleasure.

Time as perceived by the user

When we experience flow, we lose track of time, and time feels accelerated. Think about the last time you really submerged yourself in a great book, and now think about the reading you had to do for your high school literature class. Most likely the great book seemed to end too soon, but you never thought you would make it through the book for your literature class. Most likely you did not get much out of the book for your literature class either because your ability to focus on something you perceive to be boring is poor. Do you even remember the title? When you are using a fast website or service, you go in, you get the job done, and you leave satisfied. However, if the site or service is slow, you’re more than aware of its shortcomings.

Many factors influence our perceptions of time passing including our age, geography, environment, and our emotions to name a few, but according to Stoyan Stefanov in his Velocity presentation, we perceive load times as being 15% slower than they actually are. When waiting for slow pages to load, time seems to crawl. When we reflect on the duration, we will remember the load time to have taken 35% longer. As demonstrated in Figure 1 below, a page that loads in two seconds is perceived by the user to load in 2.3 seconds, and a page that loads in 15 seconds is perceived by the user to take 17.25 seconds. Later when discussing your site with their friends (and they will), the 15 second load time becomes 20.25 seconds (or basically forever).

Web performance and psychology: Time as perceived by the user

Figure 1. The actual, perceived, and remembered load times as experienced by the users.

How fast is fast enough to maintain flow?

Keeping users happy and supporting flow requires super-fast responses that may be elusive, but they certainly aren’t impossible. Of course, every person is different, but studies continue to support the two seconds or less rule. In a usability study reported by Jacob Nielsen, in his book Usability Engineering, there are three key points in time to keep in mind:

  • A user feels a response is instantaneous at a .01 second.
  • A user experiences uninterrupted flow with 1 second response times.
  • Once response times exceed 10 seconds, user attention suffers breaking flow and frustration rises.

Of course, .01 seconds is possible for tasks like typing where the text appears on the screen the instant you press a key on the keyboard. With the latency on the web, up to two seconds is considered fast enough unless you’re Google (Google wants their search results to load in 1 second.). Two seconds is still a very difficult goal, but many content-rich sites manage to either meet it or simulate it. By using resource hints like preload, optimizing images, and compressing JavaScript and CSS files, you can improve load times and improve time to interactive dramatically. A site that successfully meets the two-second goal can expect lower abandonment rates, lower bounce rates, improved reputation, and increased revenue.

What happens when we break flow?

The problem with flow is that it is a fragile state. Interruptions and distractions can pull us from our concentration, therefore, breaking flow. Achieving the state again is difficult, and in some cases can’t be reclaimed for a particular project. Slow application or page responses can break flow leaving users frustrated and even angry.

Poor performance increases user stress and hurts brand reputation

Tammy Everts, in her book, Time is money, reports on a study conducted by Foviance. Foviance measured brainwave activity while participants completed tasks using either a 5 MB or 2 MB connection. Test participants that used the 2 MB connection had to concentrate 50% more when completing the tasks, and they were more likely to experience stress during the search and checkout activities due to the slower speed. Slow web performance increases site abandonment (40% abandonment rate at three seconds), and 75% of users that experience slow, freezing, or crashing sites will not buy from the site.

Poor performance reduces revenue

Besides breaking flow (tied directly to user satisfaction) poor performance hurts reputation and reduces revenue. Stressed and frustrated users don’t stick around. They abandon carts, bounce back to search results (hurting your SEO), and 79% of users won’t return to a site where they had an unsatisfying experience.
Other studies support the impact that performance has on revenue and user retention.

  • Amazon lost 1% of sales for every 100 ms increase in page load time.
  • Google experienced a 20% decrease in ad revenue with a half-second increase in page load time.
  • Bing found that a two-second delay in page load times led to 1.8% fewer queries, 4% loss in user satisfaction, and a drop in revenue by 4.3%.

The above data is based on the actual page load times as measured by the researchers. Users, on the other hand, perceive page load times to be longer than the actual load times.

Gaining competitive advantage with improved performance

So you have worked out your performance budget, optimized your content, and your site is now just as fast as your main competitor, but your key metrics still aren’t where you think they should be. Why? Assuming that you have highly desirable content, great SEO, and a great product, your customers may not be noticing the improved performance. Bouncing back to psychology and user perception, you need to do one more thing to begin winning back users from the competition—become even faster. If a user has established a trusting relationship with your competitor and they can’t detect a noticeable difference between the performance of the competition and your service, you still lose. To win them over they need to see the difference, and for users to see the difference, you need to be 20% faster than the competition.

Weber’s Law or Fechner’s law (Weber-Fechner law) in the area of psychophysics relate to human perception of change. The laws answer the question, “How much does a stimulus need to change for humans to perceive a difference.” Weber’s Law or Just Noticeable Difference says that for someone to perceive a difference or change between two things requires a change of 20% (see Figure 2 below). So if you’re comparing your site speed to the competition and their page loads in 4 seconds, your page needs to load in 3.2 seconds for users to notice the difference.

Web performance and psychology: visual example of Just Noticeable Difference

Figure 2. The top row shows a progression in visual change as compared to the square below.

Why does it help to be 20% faster? Faster translates to mean “better” in the mind of the user. In a Radware study, two groups of users experienced the same site at different speeds. A difference of half a second was enough to influence the users’ opinions of the site. Those that had the faster connection saw the site as friendly and attractive while those on the slower connection found it frustrating and described the interface as tacky.

Take away

We as humans don’t just want speed; we need fast applications and websites to support concentration and focus. Sites and applications that respond within 2 seconds help users establish and maintain flow while longer times inhibit it. When performance hinders flow, users become stressed, and their opinion of the brand or product diminishes. By supporting flow, you provide an optimal experience that improves customer loyalty that translates directly to revenue and competitive advantage.

Your website, API, or web service can experience performance hits at any time. With continuous synthetic monitoring, you will know the minute your service experiences a performance problem. With effective Performance Monitoring, you can spot trends, and identify third-party elements that have a negative impact on your users’ experiences. Real User Monitoring will monitor actual user experiences and give you detail-rich reporting that allows you to identify locations, devices, browsers, and operating systems that give your customers grief when interacting with your content. Do your business and your customers a favor and sign up for your free, no commitment Uptrends trial.



Sources for this article:

Akamai. (2009, September 14). Akamai reveals 2 seconds as the new threshold of acceptability for ecommerce web page response times. Retrieved from Akamai:

Csikszentmihaly, M. (1990). FLOW: The psychology of optimal experience. Retrieved from Oregon Department of Education:

Everts, T. (2015). Time is money. Sebastopol: O’Reilly Media.

Google. (2018, January 9). Mobile Analysis in PageSpeed Insights. Retrieved from PageSpeed Tools:

Lindberg, O. (2018). Build Faster Websites. Nottingham: HeartInternet.

Miller, R. B. (1968). Response time in man-computer conversational transactions. Retrieved from IEEE Computer Society:

Nielsen, J. (1993). Usability Engineering. San Francisco: Morgan Kaufmann.

O’Reilly. (2010, June 24). Velocity 2010: Stoyan Sefanov, “Psychology of Performance.” Retrieved from

Ron Kohavi, R. L. (2007, September). Online experiments: Lessons learned. Computer, pp. 85-87.

Uptrends. (2018, April 18). Improving web performance with browser hints and preload. Retrieved from Uptrends:

Vieira, L. (2014, October 3). The perception of performance. Retrieved from Sitepoint:

Wikipedia. (2018, May 4). Weber-Fechner Law. Retrieved from Wikipedia:

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