I think that, as humans, we collectively underestimate how BIG a "small" number of things can feel. There's a few things here. One is that we ruminate stuff that happens, so events might mentally feel several times longer because we keep thinking about it.
Motivating example: I now nod to people that I see in several of my new classes this quarter. In just three classes, people feel like old friends. That is really fast. Maybe social experiences are the outlier here, but I don't think so.
Something about how the numbers from 1-20 are actually pretty big. Nate Soares has a thing about this, too. Like, in the entire quarter, I have at most 20 weekends, but it feels like a long time. Most vacations that people take are typically 7 days or less.
There's also a weird bias here because "days" and "seconds" are the default units of time, I think that they're supposed to be "short". But people can respond ot stuff at over 60 fps, which is some evidence that maybe the correct unit is something like 10 milliseconds.
In the case of a day, we actually go to sleep, so it does seem like a pretty good way to break things up.
But the concept of a week, I think, is far too long. Because we think in terms of weeks, it feels like they're a small building block. But a week is a long time!
Maybe this also applies to other things, like eating. (Eating 3 sandwiches is a lot.) And reading (reading 10 pages and really getting the value out of it is a lot).
Perhaps related: gradualism isn't that gradual because small changes aren't that small because our sense of scale is all messed up.