Creativity involves variability— different ways of doing things. But creativity also involves constraints, which can either promote or preclude creativity. This simple, yet extremely important and non-obvious insight is the basis of Patricia Stokes’s excellent book "Creativity from Constraints: The Psychology of Breakthrough". Through an impressive array of examples, she makes it clear that constraints play a role in many different creative domains, and in many of the most revolutionary creative products of our time.
By using constraints, reliable responses are precluded and novel surprising ones are encouraged.
What are these constraints? Some constraints promote creativity, whereas others promote conformity. Responses that are applied in an almost algorithmic fashion (e.g., rote memorization of ideas in school, copying correctly, etc.) promote conformity. Constraints that preclude low-variability, tried-and-true responses, while at the same time promoting high variability, novel responses lead to creative breakthroughs.