What are you good at? Really?

I won't say what is making me doubt myself, but there is definite doubt.

As I think of everything that I'm good at, it's all subjective. I'm smart- but that depends how you define intelligence. I'm good at filmmaking- but thats really for the audience, ignorant of the specifics of filmmaking, to decide. I can write- or what says the reader? I'm pretty funny- but.. am I, or do I just make myself laugh? I'm a good musician- but does hitting right notes make me a musician? I'm very fast- or I was, nearly 10 years ago.

The only quantifiable thing that I was ever good at was running, and that is no longer relevant. Since everything I'm good at is subjective does that mean I have to look to the consensus to tell me if I'm really good? Otherwise, I'm just another no talent reject who thinks he's a big shot. Doesn't seem like a very fair system.