White men have never had so high a conception of politeness as this, but we still consider it necessary to smile throughout a dull party so that when we get home our jaw muscles ache. Having learned to smile in order to conceal boredom, men tend to use the smile to conceal other less innocent emotions.
Source: "On smiling" [From: Mortals and Others: Bertrand Russell's American Essays, 1931-1935, v.1 (1975)]
More info.: https://russell-j.com/SMILING.HTM"