Believing we are either giving 100% or we are giving nothing. I've either got what it takes or I don't. I can do it or I can't. Black or white. No in-between.
The problem with this kind of thinking is it leads to quitting, to beating ourselves up, to chipping away at our self-esteem.
All-or-nothing thinking prevents us from growing, adapting and generally enjoying anything that isn't perfect.