Some people can fly but they have forgotten how to fly . So they forgot
Some people completely do not know they can fly . So they never learned
Some people have flew before, but forgot how to. so they never remember.
Some people know they can fly, but never try because they are surrounded with fear. So they quit
Some people wanted to see others fly before they fly. So they wait
Some people are waiting for a mentor to teach them how to fly. So they wait
Some people flew before and fell down. So they claimed that flying is dangerous and useless. So they whine and fret

BUT_
Some people are flying everyday , looking from the sky , overseeing everyone who is not flying just because they take a step to fly_