tugger, I believe you have your threads mixed up. You mentioned calling AJ oop. while here we have KJs in the CO. That is hardly the same thing. But to touch on both. In both cases, whether you are raising KJs here with two limpers and good position or calling a BU raise from the BB with AJ, essentially what you are doing is putting money in the pot when your hand is stronger than their range. AJ is way ahead of a BU steal range. Likewise, KJs is way ahead of a limpers range (they limp 76, K9, KT, JT, etc). So playing a hand when you have more equity on average than the villain is going to result in profits, assuming you play the hands correctly postflop. The less postflop skill you have, the more you can pass on what might be marginally correct calls preflop because you tend to make mistakes postflop.

Keep in mind not every raise is the same, so just because you call AJ from the BB against one villain or one situation, this doesn't mean you should call it against everyone. I insta muck AJ from the BB against most UTG opens. Whereas, if someone is opening on the BU, then I would rarely fold it. Two totally different situations.