This is a 1970s-era British anti-smoking film. Fascinating throughout. But fast forward to 4:31 to see an interview with a vice president of tobacco giant Philip Morris.
If you believed smoking kills, the interviewer asks him, would you keep selling cigarettes?
The executive's answer is a vivid illustration of how self-interest and commitment to a belief can delude people. And how neither intelligence nor knowledge are enough to defend against delusion. After all, this is clearly an intelligent man who, as he says, has probably read more of the evidence than those silly scientists who think smoking kills.
What does act as a defence against delusion is psychological awareness: an appreciation of one's own biases and how they can skew perceptions and conclusions. This man is oblivious to his biases. And so, as he proudly notes, he is so convinced smoking is harmless he permits his children to smoke. Very sad.