One of the nice things about financial stability is the luxury of not having to worry about exact bank balances. So long as the amount in the bank is even slightly more than the amount needed to cover monthly expenses, plus the minimum balance to avoid fees, everything is covered and there are no fees. It's like having a cushion - I can make small accounting mistakes on my home ledger, not notice that it doesn't exactly match what the bank says, and it won't hurt me. If it's a big cushion I might not even notice at all.
Last month I removed most of my cushion, thinking it ought to be hanging out in savings where it could earn some interest. Today I received my monthly bank statement. There were fees on it. It turns out I have $212.33 less than I thought.
Furthermore, it's been that way for well over two years.
It isn't one big thing I forgot to write down. It's lots of little things. Probably all "withdraw quarters to do laundry." I've dug back to the end of 2004 in bank statements, and I think it's time to give up and do what a friend says: record it as "experience."