I recently noticed an interesting phenomenon in my world of design. When I begin a new design project, I am focused on meeting every one of the client's needs. But when I get to work, an interesting thing pops into my head: "Now what?" It's not that I feel incapable of getting the job done, but that space of time between establishing the project and getting in to a productivity groove is difficult. It's where I have to stare "creativity block" in the face and try to drum-up some ideas.
It's in this odd juncture (and you only know what I'm talking about if you've been there) that I believe we start to meet a few of our own design needs in order to satisfy the customer's. What we design, no doubt, has a direct correlation with:
The best part about all of this is that it's okay. We can still please a client and earn an honest buck while advancing our creative credentials and sating our design curiousity. I long for the day when "creativity block" is no longer a factor, and I have ideas spewing out my ears at any given time. If anyone has figured that one out, speak up. Otherwise, I'll keep seeking drug-free ways to stimulate my mind.

I think this applies to more things than design. Your mind has the tendency to keep its most recent events up front in a more accessible location. It's not like you approach a conversation and say "You know.... I'm going to start this conversation off with a piece of poetry, even though I have never read or cared for poetry." You tend to do things like you usually do.
Branching completely out into something that has never been done is hard to imagine. If it were easy to imagine, we'd do it all the time. For the most part it seems that we create the newest ideas by putting bits and pieces of other things together to form something new.