Actors don't "act"
90% of an actor's work is preparation (memorization is just a tiny part of this- a big part of it is studying the scenes and figuring out the character's realizations and decisions)
By the time you're performing, you shouldn't have to think about the scene or dialogue at all, but just connect with your scene partner and let them guide you through it. Acting isn't about you. You're not important, it's about the moment that's in between you and the people you're performing with.
indeed