Right here, right now we are 100% accountable for what we believe about ourselves and other people. Sure, you may have experiences in the past when you were small where you were influenced to believe something about yourself, and that is the past. Right now is all you have and right now is when you decide if you will stay in that belief. If you believe you are a failure, that you are stupid, that you are wrong, too old, too weak, too ugly and that does not serve you, stop believing it. Notice that believing it and thinking it are too different things. And yes, saying these things too yourself may still happen from time to time, but you have the power to believe yourself or not. When your way of being is of fear, judgement, resentment, and reaction then you take yourself seriously and believe these things that you say to yourself, about yourself. When your way of being is from power, lightness, joy and possibility, you may say the same things and then you simply laugh and say "that is not true".
Now is the time to take a stand for yourself, against yourself. If you do not want to feel a certain way about yourself, then don't! Stop believing the lies you keep feeding yourself, lighten up and choose a new way of being. Choose what you will believe and be it!