Preparation not only has diminishing marginal returns, it has – for most people – negative returns after a certain point.
If you’re going to give a speech on Friday, you should practice. You should practice until it sounds natural and you can deliver it while paying more attention to your audience than to yourself or your words. And then you should stop.
If you practice it four thousand more times beyond that point, you’re going to make yourself worse. You’re going to get in your own head, words are going to start sounding weird, you’ll get distracted by minute changes at the actual event, etc. Someone will cough and you’ll lose your whole rhythm because it didn’t happen exactly as you rehearsed – rehearsed so many times it wore ruts in your brain.
Some things, most things, only have so much of a range of possible results anyway. If you’re giving a toast at a buddy’s retirement party, there’s no way to do that so well that they build a statue of you or so poorly that your buddy has to go back to work for five more years. I’m not saying it doesn’t matter, I’m just saying that you can reach the maximum level of “good” it can be pretty quickly.
That’s a valuable lesson in itself. Figure out the maximum positive result that’s realistic, practice until you’re good enough to hit that result, and then… go do something else. The minutes of your life are finite!