Making a film series like The Hobbit is a huge commitment. If you doubt it, just ask Ian McKellen, who briefly considered not returning to his role as Gandalf before realizing the reason he had to return.
Yes, it's true: Sir Ian very nearly passed on recurring the role in which he gets to play the best wizard this side of the Shire. Sounds like blasphemy if you don't think about it, but the reality is that being Gandalf sort of, kind of takes over your entire life. Says, McKellen, "A two-year commitment to The Hobbit would keep me from other work and keep me away from home and friends in London." That's the kind and abbreviated way of saying, "I'd like to have a life, thanks."
And since, in his own words, Sir Ian felt "I like new challenges and I've already played Gandalf the Grey," what was it that made the sacrifice worth it?
"What clinched it and made up my mind was the advice of a wise friend: 'Ian, all those fans of the LOTR aren't going to understand or care about your doubts. They just want to see you back as Gandalf.' And then I realised what I'd known all along, that I couldn't bear to think of another actor donning the pointy hat and grey robes."
So there you are! He did it for the fans. And vanity! But mostly for the fans.
(via Bleeding Cool)