Progress bars are lying to you
Brace yourself. I'm here to tell you the majority—if not all—of the progress bars you've seen have been fake. Lies. Phony. Bogus. I know this because I am Oz.
I remember the first time I heard this, a friend who worked at Apple—who will remain unnamed—told me 100% of progress bars on iOS at that time (~2013) were fake. Meaning they had nothing to do with your actual "progress".
In 2012, I was placed in charge of designing a progress bar for a client project. I set off to learn and research how to design the best possible progress bar. Quickly I learned it was a simple three step process:
Guess how long the operation will take.
Design an animation that takes that long (and looks real).
Convince yourself you’re not an awful person.
I was disappointed to learn that these progress bars were not accurate. And most of the time, the information was fudged to give you the feeling that something was happening being the scenes.
Why couldn’t a designer just show the actual information? Well, it likely doesn't exist. We don't always know how long something will take. It's dependent on upload/download speeds. It also depends on how many other people are on the service you're using, and even how many people are using the service that your service is using. There could be hundreds or thousands of interconnected operations operating in parallel. All of which, we don't know the duration of. So in a lot of situations, we have to guess.
It turns out, that Domino's pizza tracker you love is fake. And if you've ever used TurboTax, you've seen a fake progress bar.
This technique is called Benevolent Deception. The reason designers use this technique is basically because: it makes you feel better. Remember, our goal with designing anything is to deliver value. This technique can give users: confidence in your application, peace of mind, and a sense of control. We don't talk about it much because the word "deception" doesn't have the best ring to it. If you’re using an app on your phone, and you see something that gives you the sense it’s working… you’re more likely to feel confident, to be patient, to find value in the end.
If it makes you feel better, the same techniques are used in a 2,000 pound transportation device you've used: an elevator. Those buttons that hold open and close the doors don't do anything. They've been obsolete since 1990.
I'm a sucker for all this by the way. I like to feel good while I’m holding the door for someone approaching the elevator. I wouldn’t recommend placing any bets on how long your "progress" will last though. It’s probably someone just pulling strings.