How Important Is Developing a Vision Around a New Identity for Who You Want to Be?

How important is developing a vision around a new identity for who you want to become? So say, i feel depressed. I like crap. I'm lazy because i have a mental illness. I can't function. I can't focus. How important is it to say, o k, i'm going to kill this identity,. and i'm going to become a positive person ikei shaping an identity of what you want to become a thing in therapy or not. It can be, it depends on what motivates you....