It's a matter of perspective. Self discipline has a certain connotation and evokes certain emotions. For some people it may be associated with negative feelings

It's a matter of perspective. Self discipline has a certain connotation and evokes certain emotions. For some people it may be associated with negative feelings built up over years of failure. Maybe your friend realized this and decided to change the game. Thinking about it in terms of "consistency" instead of the dreaded "self-discipline" evidently worked for him, and he may be sticking to his guns in the argument because he doesn't want to fuck up the mental hack that been working so well.