Poker can be very frustrating at times and the desire to have straightforward answers is understandable. But, you are simply playing the wrong game if you are expecting black/white answers.
"It depends" sucks as an answer, but 99% of the time is true.
As important as anything else is table image. Both for you and the villains you are up against. And don't confuse YOUR vision of your image with that of the table. You may think of yourself as TAG (or LAG or whatever). Hell, you may even be most of the time. (I suspect not many people would proudly say "I'm a nit" or "I'm a calling station", etc) But how the table actually views you and evidence you have on the villains really alters how you respond to situations. (or should)
Back to your JJ hand...
I no longer can play online
, so my answer is more live based. But, one of my biggest issues is losing too much when I have overpairs to the flop. I used to suck at those situations, but I"ve progressed to being bad at them! In a standard situation like one of the others posted above (JJ w the $25 pot going to the flop), I agree with the reasoning on finding a fold usually. Most people live are not going to play a HUGE pot without a HUGE hand. Unless you have a strong read (not wishful thinking) or have enough information from previous hands that the villain will do so, find an easier spot. That said, taking that line is exploitable by a really good opponent. Which is yet another reason why, when I'm playing live, I try to identify the good opponents and avoid them!
Btw, one quick point on my previous online play...
From reading these forums, I now know how big an idiot I was to be playing online without any tracking software as an aid. Back then, i could win at 10NL, but was hit or miss at 25NL. I'd occasionally play 50 or 100, but would get smoked sooner or later. While my play has TONS of room for growth, I also realize how much of an information disadvantage I was at. Hope my donations at those levels went to some of the good folks on here.