The reality of human perception is that we never have absolute knowledge and can only operate on a framework of assumptions; when two possible assumptions are mutually exclusive, we often pick the most likely candidate and focus on that scenario.
This seems to be a reasonable methodology throughout most of human evolution, where decisions more often needed to be immediate.
In a modern world though, it seems like a way more helpful mental model is a superposition of scenarios and adequate responses to any of them; in conclusion, the only reasonably principle on which to make decisions would be maximizing the probability of being adequately prepared for the outcome of a situation, which can be simplified as "Be prepared for as many likely outcomes as possible", or, more correctly, act in such a way that maximises the sum of the probabilities of all the outcomes you are adequately prepared for.
EDIT: I probably should have read the entire article before writing all that; just one paragraph after where I had stopped the author actually makes a very similar point.