Creativity

Creativity is the use of the imagination of original ideas. (Dictionary.com)

Why is it that when you are forced to be creative your brain puts up a block and your creativity goes out the window? I was recently given a counterpoint photography assignment where we had to use our creativity. We were given two weeks and five counterpoints to take pictures of. The counterpoints I was given was straight and curved, synthetic and natural, colored and bleached, intimacy and distance, and continuous and intermittent. As soon as I was given my counter points and I was told to be creative my brain immediately put up a mental block. It took me almost the whole two weeks to even come up with my ideas to take pictures of. I could never come up with an idea when I sat down to work on the project I would get my ideas either at work or during the middle of class so I had to stop what I was doing to write down my ideas.

So why is that when your forced to be creative you can't?