Oddly enough, this makes sense.
Typically, when one things of creative settings, one thinks of the open sea, or an endless skyline, or a blank canvas. All of these things have one common theme between them: endless possibilities.
However, if we really need to think creatively, we almost need to have some boundaries. Why? Well, one reason could be that the idea of limitless opportunities (or a “blank canvas”), kind of causes our brains to freak out. You know how the hardest part of doing a project is actually starting it? It’s like that.
While our minds would like to believe they’re ninjas of abstract thought, in reality they lack a little without much-needed constraints.  We’re not really creators, but great adapters. When faced with a problem, humans like to figure out how to fix it. Not create something totally new.
Innovation isn’t really anything about creation, but rather finding solutions to existing problems (IE Constraints).
Once we wrap our minds around that concept, we can start addding constraints to our work. Scot over at Pimp Your Work gives a great example of adding a little constraint to whatever it is you do.
Being a photographer and being able to creatively shoot pictures of anything is limiting of your creativity. Instead, shooting only sunsets Pimps your creativity.
 37Signals entire business was built on this concept. They believed that they created better solutions to problems quicker by having constraints on time and money. I don’t think I need to say anything about how that worked out for them.
The worst thing you can do to stifle creativity is start with a blank canvas. Instead, try zeroing in on one problem or aspect, and figure out how to fix it.