If you start with the understanding that chocolate is a possibility (...) then you are effectively punishing yourself 3/4 of the time.

This seems counter-intuitive to me. I do like chocolate, a lot, so I do not eat chocolate every chance I get -- that wouldn't end well. I have to pick some way to choose when I get chocolate, and my usual method (and any proposed method that may involve dice, really) denies me chocolate more than just 75% of the times that I would like chocolate. So why not use an arbitrary but useful method of choosing when I get chocolate? I'm not going to be very disappointed when I roll "not chocolate", because I am usually in the "not chocolate" state by default...

On the other hand, I do understand why this system might not be good; increasing chocolate intake is not ideal, or I would be doing it anyway. So this reward system should be short term, not long term. But I think it would be motivating (for me).