I've found that some of the best outcomes come from, counterintuitively, accidents. The adjacent possibilities that we often unwittingly limit ourselves to are the obvious and already visible ones. They come from inside our heads. We have already had previous experiences that provide us with a library of possibilities. However, no matter how many experiences we have had, there are always vastly more possibilities that reside in darkness, outside of the realm of our experience. In fact, through Jan Chipchase's conception of the learning curve ("A Year of Reflection"), we see that our experiences actually open us up to an ever-increasing pool of adjacent possibilities. The more we see, the more we know is out there that we can't yet see. The trick is in finding ways of accessing these currently invisible possibilities. And yes, it's scary, because the unknown is always scary (or perhaps seemingly irrelevant, which is probably the more dangerous of the two sentiments).
When it comes to design, allowing oneself some room to play, to just do things that don't seem relevant or productive, allows you to punch into the darkness and feel around a bit. It's true that most of that kind of exploration may be seen as fruitless, but every once in awhile, you'll trip over a gem more valuable than anything under the lamppost of your previous knowledge.