Basically because we're too heavy compared to how strong we are. Oh, and not having any wings doesn't help.
they can fly if you have red bull
penguins cant fly, and chickens cant propperly fly!
fruits cant fly...........
no he cant fly he is to heavy
you cant fly it is not posibble
you cant fly it is not posibble
till it cant fly
Penguins cant fly.
batman cant fly he glides using his cape so no he cant
He cant fly because his balance would be bad, they cant fly
you cant...... -_-
A fox cant fly!