This is similarly true for finishing a degree. Luckily, that occurred to me before finishing a degree, because that did feel futile. But finishing a degree proves that you can finish stuff. That's valuable proof for yourself and when you need to give an impression.

The topic itself really doesn't matter that much -- which is also good, because then you can freely choose it to your liking, if possible.

TL;DR: I think this is very helpful advice to people who question stuff.