You're far more likely to screw up after about 40 rolls of film when you feel like you have it all licked and you don't label your containers well so you pour in the fixer first. (Three guesses how I know that!).
There is nothing like that feeling I know. In my case I was about to move 6 sheets of film to the fixer, but there wasn't a tray there. I'd spent 13 minutes in stop bath.