We seem to associate certain behaviours and patterns with categories of identity, and changing those behaviours in yourself implies an acceptance of that “other” identity.

I remember this distinctly about 20 years ago when I thought about not eating meat anymore. Choosing not to eat meat was easy, but “becoming a vegetarian” felt alien, and took some mental effort. I didn’t see myself as “one of those” people.

I suspect it has a lot to do with how important group identity is to us, as social primates, and how we tend to package one behaviour with a bunch of others. It’s like doing pushups will suddenly make you a “jock” (and maybe the irony is that, to a certain degree it will, as these thing tend to turn into slippery slopes).