My psychoanalysis is this - you withdraw because you have been winning and are feeling confident enough to start again with a small
bankroll. After all, you did it once so you should be able to do it again, right?
Wrong. The problem is - most of us don't have a lot of control over whether we win or lose. Luck is usually the determining factor. BUT, you are playing as if that isn't the case. We all do it. Everybody says be aggressive. Well, that only works at a table full of passive nits. And that just doesn't happen that much. The rest of the time your 2nd/3rd best hand or your 8/9 out draw gets played against and beat by better. AA is an underdog against 72o on a 72X flop.
So, my advice is, if you withdraw - continue playing at low enough stakes so that your reduced bankroll can survive the inevitable peaks and valleys. The valleys ARE INEVITABLE and are most noticeable when your bankroll is short.