I am constantly doubting myself, even in the face of objective data to the contrary. One big one is my academic success... I have a 3.85 GPA, I won "undergraduate student of the year in the psychology department," was the Treasurer and then President of the Psi Chi Honor Society chapter at my school, won money to buy our department an EEG for research, got my original research accepted as a poster presentation to a national psychology conference... and yet I still doubt myself as a student and constantly worry that I'm not going to be able to get accepted to graduate school. None of it feels like "real accomplishment" to me, for some reason, like it doesn't count somehow. My friends constantly remind me to stop being so self-critical, but for me, the self-doubt always comes down to feeling like I "could have done X better, or Y better." I think it stems from feelings of inadequacy for me. The self-doubt also becomes paralyzing at times, out of fear of making the wrong decision. This has gotten me into trouble mainly with deadlines for school papers... for the second time now, I've had to take an incomplete because I couldn't decide on a topic to write for a final paper because everything I came up with I just doubted would be "good enough!" I also lost out on an awesome research job opportunity because I doubted myself being "good enough" to apply, even though two professors had written me outstanding letters of recommendation and I more than met the qualifications. I ended up never applying. You're definitely not alone in your frustration and feelings.