The Wheelbarrow Principle

So I made mention of what I was going to call the MacGyver principle, but I think the best pop culture reference for this idea is The Princess Bride. Slightly abbreviated:

And our assets?
Your brains, Fezzik's strength, my steel.
That's it? Impossible. If I had a month to plan, maybe I could come up with something, but this....<shakes head> ... I mean, if we only had a wheelbarrow, that would be something.
Where did we put that wheelbarrow the albino had?
With the albino, I think.

Consider that you are Westley. You have an objective. There is no partial success, either you succeed or you fail. The objective cannot be achieved without a wheelbarrow. Now we’ll deviate from the story a little bit. Assume that Westley cannot know if he will have access to a wheelbarrow yet. He is making his plans, and he will meet with Fezzik and Inigo at the castle. He has no access to a wheelbarrow, and no way to communicate his need to Fezzik and Inigo. What should he do?

Let’s outline two possible actions. In the optimistic course, Westley assumes that a wheelbarrow will be available. Maybe he finds one on the way to the castle, or Fezzik and Inigo bring one. Whether he succeeds or fails depends entirely on whether he happens upon a wheelbarrow. In the pessimistic course, he assumes he cannot get the wheelbarrow, so he … fails.

Westley is never worse off by assuming he will find a wheelbarrow. Sometimes he is better off. Assuming that he will find a wheelbarrow is always at least as good as not assuming. So now we are ready to formalize.

The wheelbarrow principle says, when an outcome cannot occur unless an unlikely event occurs, and this outcome is important,* you can assume that the unlikely event occurs.

So if you are treading water in the middle of Pacific, you will die unless someone happens by, either a boat or a plane. The correct course of action is to assume that someone will happen by, and make your plans to maximize your survival given that assumption. So, when a boat or plane comes by, be sure you are ready to signal it.