I've never understood the origin of the phrase, "keep a stiff upper lip". Presumably it's something to do with avoiding crying (as it means to remain stoical), but if anything it's the bottom lip that may wobble before one cries; generally the upper lip always stays stiff anyway. So, why do we say this to indicate stoicism?
As reported from the Online Etymology Dictionary, keep a stiff upper lip is attested from 1815.
It is probably referring to the facial mimic, in the same way bite one's lip and curl one's lip do.
The meaning of a stiff upper lip reported by the NOAD is "a quality of uncomplaining stoicism."
Senior managers had to keep a stiff upper lip and remain.
From the Phrase Finder:
Remain resolute and unemotional in the face of adversity, or even tragedy.
This is such a clichéd expression that it is difficult to imagine doing anything else with a stiff upper lip apart from keeping it. It is similar to 'keep a straight face'
Hope that explained why we use it.
I once read that the phrase comes from a time when dead sailors were sewn into canvas shrouds. Because it was also common for sailors to try escaping by pretending they were dead, the needle was put through their lip at the last stitch to see if they responded, showing they were really alive. There must be more to the story because how would Anyone survive if they were just buried at sea.?
I have heard, on relatively good authority, that this hearkens back to when the British had military forces in Pakistan. The arms they used were single-shot rifles which had to be loaded similar to an old musket, but with the powder in a paper cartridge. Before putting the cartridge in the barrel the soldier had to tear off a seal on one end with his teeth. But if he was missing his two upper front teeth he could not do this and hence was not qualified to be on the front lines.
Supposedly some folks figured out that if they knocked out those teeth they could avoid service in Pakistan. But of course the missing teeth resulted in a lack of stiffness of the upper lip.
So "Keep a stiff upper lip" came to mean "Have courage".