I have had this problem throughout my life, and it's really starting to affect my career as I get older.

I never feel like I can say that I 'know' something. I can have years of experience in a field, but I still don't consider myself an expert.

Other people don't seem to have this problem. They may be far less familiar with something than I am, but they are not afraid to loudly proclaim their expertise, so they get jobs/kudos/whatever, while I sit on the sidelines sort of frustrated.

Does anyone else feel like that? Have you found any ways to get over these feelings?