Peter Drucker, the leading management thinker of the 20th century, had a little noted idea referred to in HBR simply as "Theory of the Business". Basically Drucker believed that every company has two or three key assumptions that determine success or utter failure. These assumptions represent the biggest risks in the business, which I talked about in this previous post, Business Model Assumptions.
Drucker's way of thinking about critical assumptions is demonstrated well by this figure from the European Innovation Institute.
To launch the iPod Apple had three key assumptions, one of which was untested and two where other companies provided evidence to reduce the risk. I think we could apply Bayes Theorem to get a better understanding of the risk.
At any point in the life of a startup, one could ask what are the 2-3 assumptions that have to be tested in the next 6-12 months. Powerful tool to bring focus to management. Also clearly highlights the skills and resources required to succeed.