All of those things help with "long-term adherence," which in turn helps with "final goal attainment."

It also helps people avoid counter-regulatory eating, or the "what-the-hell" effect.

The what-the-hell effect: After breaking one small dietary rule, people give up on the diet as a whole and think, "I've already failed once today. Might as well give up on the week."

This study tested dieting, but the authors say the logic applies to a variety of tasks.

So remember: It's OK to cheat as long as it's part of the plan.

This video includes clips from Universal Pictures and Tri-Star Pictures and images from Getty Images. Music via Frenic / CC BY 3.0.