"The getting stuck is a very important part of the process. I know younger people and students often feel that if they get stuck on something they're working on, that it's time to give up; that they don't have what it takes, they don't have the talent, they don't have the patience, whatever. But I have found that getting stuck is a very important part of the creative process. That when you're stuck, your subconscious mind is catalyzed and you actually do a lot of very good thinking that you wouldn't have done if you weren't stuck."
From an interview here.