It depends on a number of variables including the effective stack size, weather you are in or out of position, and the size of the 3-bet. If someone min 3-bet you, the optimal strategy is to never fold any hand, that was good enough to open in the first place. But if you open to 2,5BB and face a 3-bet to 29BB, then the optimal strategy is to do a lot of folding and only continue with very strong hands.
Also I dont aim at playing "optimal". If I have information about my opponents, then I will adjust based on that information. If for instance I open AQs from UTG and get 3-bet by CO, I would usually call. But if that player has nitty stats like VPIP 11 / PFR 8 over 378 hands, then I will fold AQs to his 3-bet, because I basically dont think, he has any bluffs in his range ever. And there is no point in playing AQs out of position against a player, who ALWAYS have either JJ-AA or AK, if his 3-betting range is even that wide.
If on the other hand I open AJo UTG and get 3-bet by CO, I would usually fold, since its a hand near the bottom of my range. But if the person 3-betting me has been playing with maniac stats like VPIP 67 / PFR 44 over 29 hands, then I am not going to fold anything to his 3-bet. Instead I am going to 4-bet him for value with AJo, especially if the effective stack size is such, that I can 4-bet jam and take away his positional advantage.
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