First and foremost, as an actor, I forgot how much film is such a different beast than stage. I feel the most important thing for an actor to do is tell the story. The most important thing for a film maker to do is tell the story. Let's cross fingers and toes that the two together are telling the same story and the actor is giving the director what they what at the right time so the story can be told and the audience isn't distracted by frivolous things. The actor can give a performance of a lifetime but the camera, sound, or lights might not catch it right. The film crew could make the most beautiful shot, but if the actor falls short, it looks amateurish.
Stage is for the moment, film lasts forever. I can do something with my face on stage if something hits me a weird way and people will forget about it in 10 seconds. When I do it during a take and the director decides to use it, that double chin is set in stone forever. When you see yourself on film, you instantly freak out and are afraid to do anything in fear that it'll look stupid on screen, but then doing nothing looks strange and you sit there pounding your head as the rest of the audience watches having no clue why you're behaving the way you are.
Nothing feels better than telling a joke five months ago and getting a laugh for it tonight. Then to forget you set up and delivered a joke five months ago, and then it get a laugh is even better. Comedy on film is complete faith. I can feel and read an audience when I'm on stage and manipulate them. On film, you have to trust yourself and imagine how it would be delivered if the audience was there when you're filming it.
Nothing like losing 17 pounds in the past month and then seeing yourself 17 pounds heavier out of nowhere and wondering who that person was the on screen.
It's all about story. Write the story, act the story, film the story. That's all we're doing kids. Changing the world with words, voice, and movement.