Do you think the things you write are dumb?
Here's a thought: even if the things you write are truly dumb (and they probably aren't, that's just your crappy attitude talking), it does you no good whatsoever to feel dumb about them. That doesn't help you get better as a writer.
Heaping criticism and abuse on yourself is counterproductive. You won't improve your writing by beating yourself up.
But you will improve your writing if you can learn from the dumb things you've written.
In fact, this logic suggests that the more dumb things you write, the more you'll learn--and the better you'll get at writing. Which means you should fail more. Give yourself difficult and risky writing challenges, fail at them, and then learn and adjust.
But please be kind to yourself. Embrace and accept that you're going to write bad stuff--lots of bad stuff--over the course of your career. Get it out of your system and learn from it.