Inadequacy, inferiority, low self esteem, what to do?

Now you get it! Welcome to being human! Those of us (narcissists) who fail to have the courage to recognize our imperfections fail to ever have the chance to grow or live in reality. Once you can tolerate sadness, then you do something about it. Psychotherapy, particularly with a skilled therapist (psychodynamic therapist), can be immensely helpful as can healthy relationships in general. Dont foget your faith.
Change. If you are unhappy - I would encourage you to not only look at possible areas of weakness but also to have the courage to see your own strengths, your potential and to love yourself.
Consider this.. "If we did all the things we are capable of, we would literally astound ourselves." Thomas Edison.