Criticism we direct at ourselves is a difficult problem to tackle. Typically, we don't even notice ourselves doing it. But if we consider what holds us back from saying or doing something important, we might discover an underlying belief, about our own capacity, or a worry about ‘what people might think.’
Cognitive behavioural therapists call these "automatic negative thoughts". They pop up automatically, uninvited, like burglars breaking into our brains and leaving a mess behind.
I find people don’t want to closely examine their limiting self beliefs, it seems depressing. But only by looking carefully can we assess them. We noticed that they only represent a matter of opinion, not hard fact. And another opinion is equally valid, if you take the time to look for it.
Any belief represents just one point on a spectrum, from negative to positive. If we believe “I'm not creative”, that spectrum might run from “I'm an idiot, nothing original ever came out of my head” to "I could teach Leonardo da Vinci a few tricks". Write these down, then fill in the rest of the spectrum, you perhaps won't believe the extreme comments. You'll probably settle on something relatively positive, because by doing the exercise you see that you have a choice about what you believe, and you don't need to hold yourself back.