The Psychology of Speed

By Barbara Bermes
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The following is an extract from our book, Lean Websites, written by Barbara Bermes. Copies are sold in stores worldwide, or you can buy it in ebook form here.

Why do people leave a website? There could be many reasons, such difficulty finding what they are looking for. But there’s a good chance users leave a site because it feels too slow to load. In this section, I want to draw some attention to psychology, and how it plays a big role in our perception of speed and performance.

What Is “Too Slow”, and When Do Websites “Feel” Slow?

As psychologist Jeremy Dean points out, time doesn’t fly when we are having fun. When do we experience fun? Clearly, it’s not when we have to wait. Who likes to wait, especially in this world of constant news and response? Nowadays, people desire instant satisfaction and have very little patience. Amazon offers one-day delivery; a cab shouldn’t take longer than ten minutes to arrive. We’ve become a society where waiting is not acceptable anymore especially when it comes to the online world. When we visit websites, if we don’t get an instant response, a competitor’s site is just a click away.

A watched pot never boils. Minutes drag when we are bored.

The problem with discussing website speed is that the perception of speed is very subjective and very context specific. What feels slow to me might not feel slow, say, to my father or my grandmother. We all have different expectations. For this reason, Chapter 3 will help us to formulate a definition of “too slow” with real numbers and data.

Maister’s First Law of Service

David Maister, a former professor at the Harvard Business School, came up with a formula for the law of service. The formula of the outcome of several years of research provides a measurement on how waiting for a specific service affects customers’ perceptions of both the service provided and the actual product.

Maister’s formula states that Satisfaction = Perception – Expectation. In the context of web performance and serving content to site visitors, this formula raises the following questions:

  • What was actually served and presented to the visitor, and did the content satisfy the user’s goal?
  • What was perceived by the visitor?
  • What did the visitor actually expect?


Imagine a situation where you visit a page and a loading indicator slowly moves from 5% to 10%. You’ll expect it to take a while to hit 100%. If the percentage unexpectedly begins to rise quickly to 95% and then 100%, you’ll be satisfied and happy, because your perception exceeded your expectation. Conversely, if the loading indicator goes up slower than you expect, you’ll experience an unpleasant feeling.

In a nutshell, website visitors are satisfied when their perception exceeds their expectation, and dissatisfied when the opposite occurs.


We need to acknowledge that the perception of website speed is a feelingsomething that is very subjective.

For example, perception refers to how fast the user thinks your website is, rather than how fast it actually is. Most of the time, that’s almost more important than the actual speed of your website.

Generally, the perception of something being slow carries negative associations unpleasantness, boredom, irritation, confusion and so on. Speed, on the other hand, is associated with success, resulting in less frustration and irritation especially where the user is kept informed of progress.

Given that your website’s loading time can be perceived as slow, it’s important to ensure that content is delivered as quickly as possible or at least that, during any delay, the user is kept busy and distracted, so that the experience doesn’t feel slow to them.

There’s a great example that illustrates the problem of perception. The Houston airport received a lot of complaints from passengers that it took too long to get their luggage. Instead of making the hard working airport personnel work even faster to get the luggage out, the airport decided to change the way passengers perceived the waiting time to pick up their luggage. They extended the distance from the arrival gate to the baggage claim sixfold. While the airport personnel were busy moving all the luggage to the baggage claim, passengers were kept busy by walking. The time for the bags to come out hadn’t changed. However, as a result of perceived performance, complaints started dropping dramatically.


In the context of performance, when servicing customers, it’s important to manage and care about their expectations. Disney has done a fabulous job in managing expectations so the customer receives a positive outcome in their amusement parks. They have lineups that show you the expected waiting times, with a rather pessimistic estimate, so that customers get to the front of the line in a much shorter time than predicted. As a result, the customer feels more positive.

So, how does this translate to servicing website visitors? We should set clear expectations by keeping them informed about the progress of their task. Show them the content they want to see in the fastest possible way; and, if waiting is required, show progress bars or other indicators to reassure them the website is still responding, and that they’ll receive the content that they requested.

Note: Respect

I’d like to mention respect, as I believe it’s an important factor in customer satisfaction. Ultimately, performance is about respect. Imagine you are made to stand in line for 20 minutes, only to find the cashier closing just before it’s your turn to be served. Frustrating, right? Couldn’t they have told you earlier? That’s where respect comes into play: the greater the respect shown for customers, the more likely they are to experience satisfaction.

Abandonment Rate: When Your Users Decide to Leave

We’ve all abandoned a service before. Standing in an unmoving line will make us impatient, until we give up and quit. We leave the queue and don’t finish the task we actually wanted to accomplish. We experience frustration and disappointment. The same can happen with websites. If users consider your website helpful and fast, they’ll stay and finish their task. Otherwise, they’ll leave your site without completing their task. Therefore, the abandonment rate is probably the safest and most honest judgement you can get from your users on how satisfied they are with your service.

There are many statistics and case studies demonstrating that abandonment behavior of users is due to poor performance. Ecommerce websites are hit the hardest. Stiff competition forces site owners to pay close attention to speed and execution. If your shopping cart doesn’t load fast enough, your users might just move to a competitor’s site.

Here are some real-world statistics and numbers that prove how important speed is in a world of invaluable instantness:

  • Amazon calculated that a page load slowdown of just one second could cost them $1.6 billion in sales each year
  • Almost 40% of online shoppers abandon a website that takes more than 3 seconds to load (Gomez)
  • 79% of online shoppers will not return to a website after a disappointing experience due to poor performance (KissMetrics)
  • A 1-second delay in page load time equals 11% fewer page views, a 16% decrease in customer satisfaction, and 7% loss in conversions (Aberdeen Group)

Response Time

Perceived web performance involves how we, as humans, experience and respond to the performance of a system.

The following graph shows how different response times of systems effect our brain, and how our brain deals with them, resulting in different emotions:

Figure 1.1. Perceived performance in milliseconds, and how our brain reacts[

  • We feel instant perception around a 100ms delay
  • A slight perceptible delay occurs between 100ms and 300ms
  • We definitely feel a perceptible delay under 1000ms (1s)
  • After 1 second, we feel that a mental context switch starts
  • After 10 seconds and more, the abandon rate goes up and the user tends to leave the site

Note: Mental Context Switch

A mental context switch happens when the user abandons the original purpose of coming to the site. They most likely are no longer interested in finishing their initial task.

While each user will have a different tolerance for delay, we can expect a scale of perception for a typical user based on the data referenced above.

The research really outlines the need to avoid any kind of delay as much as possible. Ilya Grigorik, a web performance advocate at Google, calls it the 1000ms time to glass challenge. In order to fully satisfy your user’s
expectation, you have around 1000ms for your content to travel from your server to the user’s glass (screen).

If you want to achieve a fast experience for your users, you need
to understand what aspects could harm such a goal.

Speed Matters: Everybody Cares, Even Google

Making users happy when your site is responsive and fast, and reducing operational and server costs by serving fewer bytes over the wire, are not the only benefits of focusing on performance. Google has made it official that their search ranking algorithm takes page speed seriously, organising search results on that basis. This goes back to a blog entry Google posted in 2010, stating that œusers place a lot of value in speed”that’s why we’ve decided to take site speed into account in our search rankings.

This is especially important when you have to deal with a lot of competitor products and websites. Being faster than your competitors definitely puts you ahead of the curve when somebody is googling for a service that you offer.

The Alexa rank measures the popularity of a website against all the other websites on the Web. Alexa’s metrics are based on page views and visitors to those sites.

Some research has recently been done on top-ranked pages and their speed, investigating whether or not the popularity of a website correlates with the
Start Render time. Start Render time will be discussed in more detail in Chapters 3 and 4, but for now, let’s say it’s a metric that records the time when the browser starts to œpaint content on the screen. It’s a helpful measurement in the context of perceived performance. If users can see content, it makes them feel that the website is ready to be browsed. However, the Start Render time only indicates that the page content has started to load, so even if users can view content, they may not actually be able to interact with it yet.

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