On a 4.0 scale here in Canada, 90+ is a 4.0. This means regardless of whether you get a 90 or a 100, you still end up with the same GPA.
I make an explicit effort not to get above or under 90. 91 and 92 is unavoidable at times, but when I get a 98 or 100, I feel like I've just wasted a bunch of time. If I didn't study much, I shouldn't have studied at all. If I didn't study at all, I probably should have gone to the exam late, etc.
In an ordinary context, I think a lot of us understand the balance between reward and effort. And of course, reward tends to come with diminishing returns as a function of effort. I really think that's the reason we all don't try very hard for everything.
...Unless there's a lot of money involved... then it's different.