This quote from Ben Horowitz's The Hard Thing About Hard Things really struck me:
Startup CEOs should not play the odds. When you are building a company, you must believe there is an answer, and you cannot pay attention to your odds of finding it. You just have to find it. It matters not whether your chances are 9 in 10 or 1 in a 1000. Your task is the same.
Almost every substantial breakthrough in my career has been preceeded by a period of time in which I had no idea how I was going to do what needed to be done. Sometimes you just need to decide what needs to be done, believe you can do it, and then will it to happen.