If you hit middle set on an uncoordinated flop, and someone else has top set, it's quite simple. You give the other guy all your money.
Can't argue with this.
Let's try to break this down.
What hands could you make this play with? You could have AA, KK, QQ, JJ or 33 definitely. J 8 would likely make this play for protection and 9 10 might move in here as a semi-bluff.
How would each of these hands behave preflop?
AA or KK you might call to trap before the flop. So these are consistent. 33, J8 and 9 10 are all calling hands on the button in this spot and so are equally plausible. QQ and JJ surely reraise preflop against most players, not wanting to let the blinds in cheap. In fact, of all the possible hands here, JJ is the one you are most likely to have reraised with preflop.
This, coupled with the fact that JJ is 8 times less likely than AA or KK just from the distribution maths makes this an absolutely must call.
Awful fold.
Great for you and demonstrates the power of aggressive play.