What we say to ourselves is critical to our concept of self. Distortions and negativity can be devastating. Allowing others to define us puts us at the mercy of another's too often misguided perception of who we are.

Challenging the veracity of what we or others tell say about us is discussed in the following sources:

Contents
Challenging Negative Self-Talk | Psych Central
Negative Self Talk: Top 10 Things NOT to Say to Yourself | NLP Discoveries
15 Common Cognitive Distortions | Psych Central
Fixing Cognitive Distortions | Psych Central

Getting better is hard. Beating up on ourselves truly is unhelpful.