Regarding gym beast - it has few effects: - you eat bigger portions - you go to gym more often - you try harder (i.e. bigger weights etc.)
I can atest that this works _for me_, but using confidence to reach a goal is quite common.
I mean there is nothing stopping one from doing all that without thinking "I'm a gym beast now". I feel that its more about breaking the mental structure one is used to, eg "I'm not good at the gym", in that case it might help, but I would argue that instead of replacing one with another why not drop it completely and just do what is needed for the goal one has set. If you do the right things the results will always follow.
"stop having low self-esteem bro" is not an constructive advice.
We human are peculiar in that our perception of things (about ourselves) often affect the outcome. "it won't work anyway..." mindset when starting usually end up being a source of self sabotage. Probably somewhere along the line with protecting ego or creating surrogate objective such as "See it didn't work. *I* was right". Creating a vicious loop.
Blind optimism have shown, to many, is a good antidote. Some enforced enlightenment or rationalist talking points usually don't