I think that sometimes when a person says they have a healthy self esteem, or ability to be assertive, it is sometimes met with judgement, oddly. With that in mind, I'll say that it is OK to give yourself credit when you've done your best. It is important to learn and accept what a "reasonable" best really is. We aren't all going to be stars or super experts. We are going to be infallible, say or do the wrong things sometimes. Everyone does. It's a matter of accepting that as more of a norm, than a failure, and just moving forward, enjoying the present, and not dwelling on the past. The past is gone and will never be again. Intent matters.

For the most part, I've always been a rather assertive person. On occasion, I've gone beyond assertiveness, which has faults. My sister (older than me) has very often not been assertive enough, in her life. Same parents. Same way raised. However, she has become a bit more assertive over the course of her life. How? Some highly difficult situations pushed it. She finally started pushing herself more (Feel the fear and do it, anyway.) The practice of all of this, and seeing positive results, increased her comfort in becoming more assertive, thus increasing her self esteem.