Money is so psychological.
One thing I’ve learned, and I am really good about, is that I do not count the money during the convention. I wait until all sales are over, then I order the money in denominations, then I count. I count from smallest to largest. This is VERY important, because the other direction is SUPER DEPRESSING.
The other thing that I have to get better at is, when somebody gives me money for a donation for Rocksalt or an advance on their electric or whatnot, DO NOT PUT IT IN WITH THE REST OF YOUR MONEY. Because you will FORGET that it is not yours and you will start thinking that you have it when you most certainly do not. Makes things more painful when it comes time to pay.