The person you are is a thousand times more interesting than the actor you are trying to be
Of course we are pretending on stage. Ideally in a believable and truthful way. But what are we supposed to act out, when we don't have a script?
Don't start pretending in a pretendingy way. Don't start inventing drama or copying things you saw in a movie or scripted theatre work.
Instead, look inside. That's where the real stuff is happening. Grab that and play that.