Loving yourself and being your own cheerleader, that's what makes you gain self-belief and confidence.
It's natural to doubt yourself and hold yourself accountable and we all end up doing it without even noticing, but when you train yourself to be aware of the negative comments you say to yourself and turn those into positive reinforcements, then you slowly become your own cheerleader.
You know what else we tend to do? we tend to say things like "Oh that was stupid" or "I look ugly here" out loud, sometimes infront of people like our family, friends or even strangers, and that's the worst thing you can do to yourself because you are painting a bad picture in your own hands to the person infront of you and you are definetly not appearing confident either.
The worst thing is saying those comments infront of children, because guess what? the children will pick on that habit and think it's okay to voice their doubts and say negative comments about themselves.
So start practicing turning that self-doubt into self-belief and train yourself to quiet that negative voice inside of your head and not make it louder.