This is Art Cognitive Dissonance. It stops us from sharing art we've worked hard on, talks us out of applying for jobs we should be qualified for, and generally makes us feel like crap.
First off, accept that the fact that you can now see all the flaws is proof that you've grown as an artist in the process of creating that piece. The flaws are good to be aware of- you can address those in your next piece!
Actionable Steps for the Future:
1. Ban "Not Good Enough" from your vocabulary
2. Focus on actionable immediate goals
3. Add 'yet' to sentences to allow for improvement
4. Acknowledge milestones, even small ones
5. When requesting critique, ask for specifics
6. Only compare yourself to your past work
7. Find aspects of the piece you enjoy, feel are successful, or represent what you've learned.
If you absolutely can't shake the feeling and continue to struggle with feeling positive about your work try:
- Developing an improvement plan that focuses on areas of weakness. Working towards an end goal will help you see your art as a journey.
- Reach out to a trusted friend for help. The wrong friends are more than happy to tear your work apart, so ask someone who's been supportive and in your corner- someone you can trust. Ask them what they like about the specific piece, and TRUST THEM. Sometimes it helps to write it down.
- Actively stop yourself when you start feeling bad about your work. Go for a walk, exercise, listen to music- remove yourself from the situation.
Keep in mind: Not all displeasure is bad! Being dissatisfied with your work can drive improvement- just harness it in a positive, productive way. Keep notes on self critique and work towards addressing those issues in the future.