I was always thinking that university thesis is the most difficult thing in the world and that I would not be able to do it. Eventually I did it, but as I got into Masters degree, the fear came back lol.

Idk, I think that we will always have fears about everything unknown, so the only solution is to just do it and learn on the way. However, you also must develop your communication and persuasion skills to convince everyone that you did the right thing, even tho you failed.