Let's just say that they are paid to do that and they enjoy far more incentives than us as it is their day to day job. When I first came out with my muscle mass diet, I learned that we should eat at fixed timings and not be afraid to add in our usual treats to reward ourselves, especially so if you are a hard gainer. I think, as with all normal humans, it is extremely difficult to keep to a fixed diet with far too little treats. You might argue that if bodybuilders can, why can't we?
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