It is hard to avoid the moments when you are disappointed about yourself and you think that you are nothing. Especially when somebody tries to underestimate you for some reasons about your weaknesses.
But nobody is perfect, no one has all good points but no bad points. Either they hate you on purpose or by accident, you should consider it as the motivation for you to improve yourself.
Besides, you shouldn’t lower yourself because of their judgements. You still have so many good points that other people always respect and appreciate you.
You should believe that you have your own values and there will be people who’s gonna realize those. Just never stop enhance yourself and love yourself.