Something I used to do that was killing my budget: I'd check my bank account balance to decide if I could afford something instead of checking my budget.
Those are two completely different things. Your balance includes money that's already spoken for - rent, subscriptions, groceries, whatever is coming out later in the month. So it looks like you have more than you actually do, and you spend accordingly.
The fix is simple but it changed how I think about money entirely. Instead of asking "do I have enough in my account?" ask "does my budget have room for this?" If you haven't allocated money for it and there's no leftover, the answer is no, regardless of what your balance says.
Curious if anyone else has fallen into this trap before. What's a spending habit you've had to actively unlearn?