Celebrity switch up

I was watching some movies this weekend with my family. There were too many to name but i began to notice that the same actors and actresses where suspiciously popping up in almost every movie that we watched. The funny thing was...it was a completely different role. Its weird how they can put on a mask for one film, be completely hilarious dropping one liners every second, and then the next minute in a different movie be someone totally different. This time maybe dark, sinister, or evil. Why do we accept this?! is it because we love Jennifer Aniston and don't care if she is the querky girl in Marley and Me or the disturbed housewife in The Good Girl. I don't have an answer but it is interesting to me. So many times i have watched certain characters in different movies and accepted their acting as who they really are. But when Angelina Jolie doesn't play in an action film i am slightly thrown off. Or when Will Ferrel isn't making me laugh i feel kind of confused. Its like we learn to love these celebrities based on the characters they play. We think we understand and know them...if we saw them in the streets they would be our best friends! DUH but when they change that in the slightest we or at least i have a hard time accepting it. Maybe the sign of a good actor is when we as the audience can never truely understand who they really are....