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A good reason to "mix it up" is a response to villains' actions.
I think you were just a bit tilted (easy to assume since you admit as much in a couple sentences).

If not "mixing it up" means...

FOLD PRE.
KJs from UTG 8-handed is just not that strong. You have to act first now and throughout the rest of the hand (assuming the blinds don't see the flop).
You'll never have TPTK, and rarely...