Do they have any studies where they manipulate people's beliefs about willpower to see if that affects it? This study has a been confound which is equivalent t

Do they have any studies where they manipulate people's beliefs about willpower to see if that affects it? This study has a been confound which is equivalent too "we asked a bunch of people if they thought they were strong. People who said yes we're stronger than people who said no! Therefore believing your strong is how to become stronger!"