I would say yes, I doubt myself constantly. It's a vicious cycle of constantly comparing myself against the big picture, love of concepts vs. execution, perfectionism, knowledge of human perception / psychology, and and how they work against me.
Big Picture: I always compare myself against the best. I might be pretty good at something. But in the grande scheme of things I might just be a big fish in a small pond. For example... I know a little bit about a lot of things... like visual design, web design, audio mixing, and video editing, music, composition, playing guitar, martial arts. When the average person sees that, they are like HOLY SHIT YOU ARE AMAZING! But I know I don't know enough to function on a professional level. Compared to people who specialize and do it everyday, I know virtually nothing. If I knew I could walk into an interview right now and apply for a job in one of those categories and get it... then I'd be a lot more confident that I knew what I was doing.
Concepts vs. execution: I hate putting in those 10,000 hours and studying / practicing / working hard. I get pretty bored. It's really hard for me to become an expert at something. Like guitar. I can get pretty technical and I know a lot about theory but I'm pretty bad at actually being able to perform full songs. I just learn lots of pieces of things and I'm always bouncing around. It undermines my confidence when I tell people I've been playing for 12 years and people say "oh play me something" then I'm like "ummm... I don't know too many full pieces" It's like that with a lot of things I do.
them: "oh you went to college for web design? can you make make me a website?"
me: "umm.. I haven't actually made too many full complete websites"
them: ????
Perfectionism: Since I'm always looking at the big picture, I tend to have high standards. What I personally like and get turned on by is stuff that masters do, stuff that's usually way beyond my ability. If I know I can't do that, then I think my stuff is not very good and I just shut down. If it can't be great then I'll do nothing at all.
knowledge of human perception / psychology: I know how limited human perception can be, so I'm never quite sure if I really truly know something. I've caught myself so many times being wrong when I thought I was right, because I made some minor calculation and sometimes I'll just remember things wrong. For instance... I was arguing with somebody about how to play a song. And I had been playing a certain way for YEARS. I was so certain it was the right way and we looked it up and I was utterly wrong. Once I saw the proof I was dumbfounded.
I had no idea how this happened, or how I could have been so wrong. In high school I would study for math tests and be like "wow I aced that". I would get them back and I would get like a c- or a d because I had made so many minor mistakes. I'd multiply two numbers I should have added, or forget to do something trivial... and it would mess up the whole thing. This has happened to me so many times in so many things it's really undermined my ability to be SURE and confident in myself.
Another example is when I was in the kitchen and I was looking for a can opener. I looked everywhere... I thought my roomate had stolen it (because he had taken a few things into his room indefinitely already) so I was about to bust up into his room when I saw it. It was sitting on the counter right in front of my face. How could I have not seen it? I guess i didn't expect it to be there and it just blended into the background. This really made my head hurt, and made me feel really shitty afterwards.
All these things just make me doubt myself constantly. Especially when I feel like I have so much "proof" to doubt myself with. I'm not sure what it would take to fix it.