Kevin Simler and Robin Hanson write about evolutionary psychology of the brain in their book The Elephant in the Brain to explain why it is that we have hidden motives and why those hidden motives can be so hard to identify. The authors write (brackets mine, italics in original), “The human brain, according to this view [evolutionary psychology], was designed to deceive itself–in [Robert] Trivers’ words, ‘the better to deceive others.'” The authors look at how self-deception can be positive from an evolutionary perspective, and how that shapes the way we think about ourselves and our place in the world.
Fudging on the rules from time to time and making ourselves look better than we really are can be good strategies to survive, or at least they potentially were for our ancestors. Humans evolved in small, political, social tribes with rules and norms to adhere to and enforce to varying degrees. Slight amounts of cheating, if they can go unnoticed, can be beneficial for survival. This drives an evolutionary pressure to pass along selfish genes that favor individual survival, hold up the rules when it is convenient, but push rules aside when it benefits us. Simler and Hanson argue that this pressure is so strong, that we evolved to not even notice when we do this.
We also seem to justify our actions (a process known as motivated reasoning) in a way which says that we didn’t really do anything bad, we were just making the best decision we could given the circumstances or we were upholding fairness and justice in the absence of a greater authority to administer justice. The more we can convince ourselves that we are right and that we are on the correct side of a moral argument, the more we can convince others that our actions were just. If we are blatantly lying about our motivations, and we know we are lying, it will be harder to convince others and build support around our actions.
If however, we convince ourselves that our actions were right and our motives pure, we will have an easier time convincing others of our correctness and of our value to them and to society. When we give to charity, at least part of our donation is probably driven by a desire to want to be seen as the person who gives to charity or as a person with enough money to give some away. These two motivations, however, would be frowned upon. Instead, we convince ourselves that we give to charity because it is the right thing to do, or because we think the cause is incredibly important. Those both may be true, but if we completely convince ourselves that we are donating for the high-minded reasons, we will be more authentic and better able to convince other people that we made donations for high-minded and not selfish reasons. We are wired not to see the world how it is, but to see it through a filter that magnifies our greatness and minimizes our faults, deceiving ourselves so we can do a better job of presenting the best version of ourselves to the world.