I've heard that saying many times. I used to be one of the people who scoffed like that too. Sometimes, I still do.
But you know what? I'm ok with that. I don't know how to do a lot, so I'll learn. I don't know how other people do things, so I'll make it up and improvise. I don't know if it is the right way to do it, so I'll adjust, fixing my mistakes as I go along.
I may not be able to do much, but I'm evolving. Which is more than I can say of some people I know.
But hey, those who can't teach, just do.