Besides the obvious ones like disease and death, loss of loved ones, things like that -
I would say it's the fear that what you can and can't do with your life is already predetermined by genetics and there's nothing you can do about it - specifically being genetically limited to being average at best, and inferior at worst - where it is a fact, that it is not possible for me to achieve at anything, no matter how hard I try, practice, work, sacrifice, etc. - that my abilities are fixed, they are what they are and that's it, I can't do much better than I can do something right now, and if it's enough to do something it's enough, and if it isn't, it isn't, and also that the best I can do is get just a little bit better at something with practice, and no more, but if I stop practicing, I'll quickly atrophy back down to my default level of ability.
And if I can't do better than average, it means I can't make money and get into a better lifestyle and get the stuff I want, and it means I can't be an interesting person or do anything I wish I could do or come up with the kinds of ideas I wish I could have, and it also means my chance of attracting someone isn't good either, because I won't be able to be successful or interesting enough to impress or interest anyone with me - which is another big fear in and of itself.
It also means that I'll never be able to push back against and assert myself against people that act like they're better than me, and that it's true that they are in fact better than me, and I have to just take the insult/humiliation.
I've always been afraid of this, being limited/average/inferior/a loser/incapable of achievement or success, because that's how I felt about myself and that's how it seemed for people around me. It seemed like you were either born good, or you weren't and that was it. Outside of the obvious ones, I'd say this is my biggest fear.
