Why does the progress bar get stuck at 99 per cent?

«Update and Shutdown» just ran on my HP work laptop. I was annoyed before the update even started, as it always takes longer than you’re told at the beginning. And, as always, the bar moved at different speeds, only to get completely stuck at 99 per cent.

But why?

Progress indicators are first and foremost good for our psyche. Imagine for a moment that you’re in line for an ice cream. As long as the line is moving and you’re advancing, the wait is relatively bearable.

For exactly the same reason, when installing programs, there are numerical or visual representations that are supposed to show you that something is happening and thus reassure you. However, this only works as long as progress actually occurs. Like standing in line: if you don’t move for a while, you get impatient and your mood gets worse.

The problem: «On the one hand, the effort for a detailed reading isn’t worth it in most cases, as it exists primarily for the mental wellness of the user. On the other hand, as a programmer, you can never really make a progress bar reliable anyway. That’s why the whole tool is implemented in a very simplified way,» says Martin Gasser, Lead Software Engineer at Digitec Galaxus AG.

The machine can’t do much more than guess

Installations are complex: files must not only be downloaded – a task that depends on your Internet speed – but also installed on your computer. And that’s often where the biggest differences lie. Downloaded files must be decompressed, which depends on the speed of your processor. Also, files must be saved and already existing ones must be read and deleted if necessary. Depending on where these files are, what state they are in, and how fast your hard drive is, this might take longer. Finally, you may need to change the settings for your new program, which in turn will be affected by your operating system.

«Unless Internet speeds fluctuate greatly or there’s even a network interruption, the duration of the download itself can be estimated relatively well, but when installing, differences are massive,» says Remo Vetere, Senior Frontend Engineer at Digitec Galaxus AG. «If the duration was overestimated, the progress bar simply stops halfway through. If the duration was underestimated, the bar freezes.»

The fact that this happens so often at 99 per cent is precisely due to this simplified implementation of progress indicators. They aren’t even «smart» enough to get stuck somewhere in the middle, he says. «Initially, the duration is roughly estimated. Then percentages are counted forward at regular intervals. If your installation takes longer, the bar simply stops at the last possible moment, i.e. at 99 per cent, until the task is completed,» Martin explains to me.

An interplay of fact and psyche

But does this really happen that much more often than installations finishing «too fast»? «Yes. It’s much more likely that something unexpected will happen than that something expected won’t.» An analogy from everyday life would then look something like this: you want to put on your favourite t-shirt, rummage through your entire closet for it, only to realise that the item is currently in the wash. This scenario is much more likely than planning to wash your favourite t-shirt, but then not having to because it’s already been magically cleaned.

Still: here, too, our psyche plays a role: «As a user, you notice when something is going on too long. If your installation takes less time, you just move on without giving it much thought,» says Martin.

So, in short, the progress bar works like this: in most cases, it’s implemented in a very simplified way, as a detailed version simply isn’t worth it. The tool is only there to show us users that everything is running in the background and to spare our fragile nerves – at least as long as the bar doesn’t freeze at 99 per cent forever.

Why does the hand of a station clock usually stop short? Why do they have popcorn at the movies? And why are drinking glasses not allowed in waste glass containers? Everyday life holds many puzzles in store, which I try to solve at irregular intervals. If you have a burning question but no time to research it, send it to me by mail. I like doing the dirty work.