It is well known that people often make irrational financial decisions even in fairly simple situations where they have all the information they need to make a good decision. I have an idea about why we are this way that is so simple that it is very unlikely to be original, but I couldn't find this idea in other writings in a quick search. One simple model of the value (or utility) of money is that each doubling of your savings has the same incremental value. So, if you start with $100,000, dropping to $50,000 is as detrimental as doubling to $200,000 is beneficial. For small gains and losses, the sizes of steps of equal utility differ by less. For example, a loss of only $1000 is as detrimental as gaining $1010 is beneficial. However, throughout most of human evolution, great wealth for a single individual did not exist. Before the advent of storing food, a large kill would only last until the meat rotted or was taken by other hungry people or animals. We are simply not ...