ABSTRACT
How old am I? Will the salmon or pasta taste better? Will I see greater returns investing in the stock market or in real estate? The answer to each of these questions has two elements. The first is the content of the answer (e.g., 39, the salmon, real estate) and the second is a feeling of certainty about that answer. It is tempting to think that understanding behaviour requires understanding the former, that is, the output of our cognitive processes. However, it is the latter, namely the certainty with which a decision is reached, that determines how vigorously we pursue a course of action or whether we act at all; certainty will determine whether we stay with our initial choice or search for another, and how we present our decision to other people. Certainty, in other words, is the arbiter of action.
