It's not who you are underneath; it's what you do that defines you."
I agree, generally.

My idea of myself (my self-image?) is subject to change due to circumstance, environment, chemical balance, etc. I may think it doesn't change, but that's a delusion brought on by the fact that the same "I" is thinking that thought. So I don't give much credence to an 'underneath' me.

My life is a continual effort to make what I 'do' match my high opinion of myself.