When you're learning to throw you want to keep every pot that makes it off the wheel because you are so pleased that it has.
The trouble is that a potter, like any artist, is always learning. You have never finished learning or you would probably stop. You may be able to guarantee getting a pot off the wheel, but now you are learning to make a different shape, or now you are aiming at 12 near-identical mugs, or now you are trying to free up your style of ...
So you continue wanting to keep everything. What is needed is a bit of discipline.
I'm quite good at self-discipline generally. I know people who are astonished that I can keep chocolate or biscuits or liqueurs or other tasty things in the house for months or even years without eating them all up. On the other hand, I am, as you know, overweight, partly because of my metabolism no doubt but combined with the fact that I do like to eat more than I need, so 'quite good' at self-discipline is probably about as good as I'll get.
In the pottery I am also 'quite good'. I am moderately strict about what is let through, but not rigorous. One thing I have always done is to follow the advice of the person who taught me most of what I know about being a good potter*, Douglas Phillips of Ridge Pottery in Somerset, and occasionally cut a pot in half to look at the thickness of the walls and base. Are they even? Are they the thickness you thought they were and is it a good thickness?
Here's one I cut up yesterday. It's a one-person teapot, one of four I made the day before. As I was rolling the base to tidy it, the centre of the base curved in. This is usually because the pot is not really firm enough for rolling the base yet and doesn't really matter in a finished pot apart from aesthetically. It can sometimes be, though, because the base is too thin. I was feeling a bit more rigorous, so I decided to cut it in half. Base not too thin, though slightly thinnner than the rest of the teapot. The walls of the rest pretty even too, and it was a nice shape, so I was pleased with what I saw. To be really self-disciplined, I think you have to not mind finding you have a cut a good pot in half. I didn't. So that was good.
* On the matter of how not to be a good potter, I am entirely self-taught.