Sometimes you take a job for the money, sometimes you take it for the location, sometimes you take it for the script; there are just a number of reasons, and ultimately what you see is the whole landscape of it. But I can tell you from behind the scenes - that's what it is, as an actor.
No man is invincible, and therefore no man can fully understand that which would make him invincible. Even with complete and thorough study there is always the possibility of being defeated and although one may be expert in a particular form, mastery is something a man never stops seeking to attain.