Because if you did you’ll never be able to do/make anything of significance.
And the worst kind of criticism is self-criticism, constantly beating yourself.
If you pay much attention to any kind of criticism, you’ll not be able to do it because fear of being criticised by others will stop you from taking risks and doing what matters to you.
What to do instead?
Praise yourself because there is lots of research supporting that praise and performance improvement are linked. And, there is a thin line between praising yourself to lift yourself up, and turning into an arrogant person.