I am reading Robert Trivers’  The Logic of Deceit and Self-Deception. It is a lot of fun and incredibly interesting – my wife keeps on nabbing it, she is enjoying it so much.

His main thesis is simple: In our evolutionary past, we had to lie a lot to get ahead, to deal with parent-offspring conflict etc. We are better liars if we can convince ourselves that we are not liars. Hence, this leads to self-deception. I was reminded of the strength of this claim today.

I set an old question to my students (not one of my own but inherited from the past cohorts of teachers). This question has been used recently by many fellow teachers and it has been taught by TAs.  I happened to look at the historical answer to the question and found a mistake. And the topic had not really been covered in class. A student then came to ask me about precisely this question. I decided to pretend the answer in the answer key was right – it would only have confused him more if I had gone into the right answer and I had not taught the subtlety in class, I rationalized to myself. A few minutes later he came back and asked me why the answer wasn’t in fact the one I had found earlier. I was found out. I told him his answer was correct too.

But the question and (incorrect) answer had been posed unchanged for 8 or so years without anyone pointing out the answer was wrong. Why was it discovered now? I suppose the student who spotted the right answer could be quite smart – and he is. But there are many smart students in previous generations who never found the right answer.

So, my explanation is really the Trivers’ explanation. I did not lie convincingly. My doubts about the answer manifested themselves somehow to the student. He investigated further and cracked the problem. In previous years, the teachers were convinced the answer was right and never even questioned it. They never had to lie because they truly believed they were telling the truth, just like the Trivers’ thesis on self-deception. Students left convinced. If they had doubts, they stifled them.

The student who spotted the error will be on the PhD market soon. I will write him a strong letter.