Flexibility is a requirement for survival.
~ Roger Von Oech
It's difficult to get your creative juices flowing if you're always being practical, following rules, afraid to make mistakes, not looking into outside areas, or under the influence of any of the other mental locks.
Remember the two benefits of failure. First, if you do fail, you learn what doesn't work; and second, the failure gives you the opportunity to try a new approach.
Knowledge is the stuff from which new ideas are made. Thus, the real key to being creative lies in what you do with your knowledge.