The thing about these studies is that while you can discover that one thing that is commonly thought-of as requiring willpower might indeed interfere with another such thing, the question of what that whole class of activities is has not been answered and indeed varies from person to person.

For one man, for example, approaching an attractive woman might require willpower while for another, it might just be a habitual response.

On the other hand, it's likely solving a difficult puzzle would requires resources on anyone's part.

This is a crucial concept and I hope that question of definition is worked on...