:(

The trouble with reward systems is that they only work if the person desires the reward more than the pleasure of whatever the reward is supposed to replacing. Sometimes, it becomes easier for the person to say "I don't need the reward that badly" and use the whole system as a justification rather than a motivation. In which case, the whole system needs to be overhauled to find a reward that is more desirable than the original behavior. However, when the behavior is truly pleasurable and the consequences not all that bad, it can be hard to find a reward motivating enough.

Or something like that.