It doesn’t serve you to deny what happened in a past experience, no matter how painful or disappointing. You can’t, for instance, change the fact that you were criticized by the teacher. You can, however, alter your interpretation of the event.
That is, at the time you were originally criticized, the meaning you might have assigned to the experience was “I’m not good enough” or “My opinions are worthless.” While this was the interpretation of a child, you may have inadvertently carried it into your adult life. Today, though, you can consciously choose to view the situation differently – for example, the teacher may have disagreed with you, but it wasn’t a statement about your intelligence or your overall worth as a person!