I agree, it is way too easy to do.
Sometimes when it's particularly bad, I make it a goal to come post or do a journal entry before I eat anything that's not on my plan.
"If you drop an egg, you don't say, 'Oh, shoot' and drop the other 11, do you?"
-Source unknown, but obviously brilliant
Reached goal 4/16/2010...but kind of afraid to look these days