Excerpt from Michael Caine’s awesome book Michael Caine – Acting in Film: An Actor’s Take on Movie Making 
If there is a fight sequence and you do it brilliantly but rip your coat, continuity says, “We’ve got to do the fight again because you don’t have a ripped coat in the scene we’ve already shot.” You even worry about cutting your face shaving. For six weeks you can’t sit in the sun on your day off because your skin color will change — no sun for you because they’re wandering about with Polaroids, comparing you with the previous scene. So you sit still and try not to change.
This is absolutely my favorite book of all time. Caine is soooooo smart about his craft and how to maneuver around it and still be honest and tell the truth. He also works more than any other actor on the planet. I think at one time, he was doing 3 film a year. Which in this day and age, is unheard of.
There is a quote, and he is very quotable, that relates to his constant working – “First of all, I choose the great [roles], and if none of these come, I choose the mediocre ones, and if they don’t come, I choose the ones that pay the rent.”
Hence The Swarm :)