I don’t know whether I’m the only one who is puzzled by this, maybe not. What I noticed is that whenever I see self-portraits of people - and some photographers do a fair amount of those - there’s never a smile. Why don’t people smile when they take their self portrait? Is smiling bad? Would a smile take something away from the portrait?
Update: A few people emailed me and told me that the reason why people don’t smile is (at least partly) due to the nature of long exposures or having to wait for the shutter. I am not sure I am willing to accept that fully - after all, many photographers go through all kinds of ordeals for photos that they really want.