First of all, stop thinking of and referring to yourself as dumb! We all have different strengths and weaknesses and part of our ability to succeed is finding the environment which matches our skills. Even though your mistake at the first job was costly, it was still just a mistake and we all make them. And not everyone is cut out to work at a fast paced environment such as McDonald’s. I’m sure you would have eventually mastered the tasks and become more comfortable if you had stuck with it, especially without the extra pressure of trying to learn in front of someone you liked.
I think you need to just keep trying and building life experience. Mistakes can lead to wisdom and competence, and ultimately to confidence. However, since you have always struggled in school, I would recommend meeting with a psychologist trained in intelligence testing and cognitive processing issues for an evaluation. It might also be helpful to take aptitude tests and career assessments so that you feel more comfortable pursuing your career goals. Depending on the results, you can then decide if you need a tutor, a career coach, biofeedback or some other type of service that will help you feel more successful.
All the best,
Dr. Holly Counts