Every time you break your own rules, you make it more likely that you will do so in the future as well. If market doesn't punish you right away - its even worse, because you'll have positive feedback associated with rule breakage.
So:
Do not break your rules. Ever. Follow your system or don't do whatever you were going to do.
If you did it anyway, and market slapped some sense into you - be very grateful. Alternative is worse long term.