Some bosses are just so huge and overwhelming that in order to get anywhere, you just have to get up on them real close. We're talking hanging onto their back hair close. Usually, you'll be attacking some kind of obvious Achilles' heel with a sharp thing, like in Shadow of the Colossus. Occasionally, the boss will employ some method to try to remove you like swatting you away or violently shaking to, very rarely, the intended effect. It is very rare that these bosses will be very agile so as to give you, the player, ample time to attach yourself to wherever you can.