Do you really think it is, when one have +3 armour and +3 gauntlets?
It is when you die with too few hits to your liking. If everytime you die, it's not because you took that unexpected hit in a duel, but you were ganked and couldn't do anything about it, then it's time to stop investing in more HP/armor.
Imagine you die with one unarmed strike. Getting more survivability sounds like a good idea. Now imagine you have zillions of HP, and the only way to kill you is to chain-polestagger you during half a minute. More HP wouldn't be very useful.
Edit : lol at pole S.T.U.N censorship.