The information I just gave you about jack-ten is one of the first non-standard tidbits a hold'em player learns about the game. It's the first adventurous hand new players learn to play. When they learn that its playable, they'll find cause to play it almost any time they can, because they're looking for another hand they can put chips in with. Most players who are learning to play reasonably well still have a little voice in the back of their head that wants them to play as many hands as possible, so their jack-tens get played every time they have them. Remember this next time you’re in a pot with a player who's just learning the game, or an experienced player, or a loose-aggressive player, or a tight-aggressive player, or....well....anyone.

That's the point. You can be against this hand at any time against any player. It's probably the most diverse hand in hold'em. It can be in an opponent’s hand whether or not there was a raise before the flop. So here's a rule I've learned to follow: always assume jack-ten is a possible holding for your opponents before the flop. I know I said it can be out whether or not there was a raise before the flop, but this applies especially to hands where there wasn't an early position raise before the flop. Another thing that makes jack-ten a dangerous hand to be against if you're a solid player is the cards that give you a pair will often give your opponents a straight draw and the hands that give you a big draw will often give them a made hand. Here's an example:

You have AK-offsuit on the button in a $3/$6 game and three players limp in before you. You raise. The big blind calls and all the limpers call, so five players see the flop of J-T-2 of mixed suits. It’s checked to the middle position limper who bets and is called by the player on his left. You call with your gutshot straight and two over cards. The big blind and one of the limpers fold. The turn is a jack. Everybody checks. The river is a queen, giving you a straight. The middle position limper bets out and the other player folds. You raise and he re-raises. If he's a solid player, don't even think about re-raising. If he's a loose-aggressive or bad player, you could think about raising, but I'd probably still just call anyway. The only plausible hands you can beat here are KJ, AJ and J9. Given the play, it's more likely you're up against QJ or JT. In no-limit tournaments, where survival is of the utmost importance, it's even more important you don't risk your stack when a player holding JT can beat you.

If you rivered the nut straight on a paired board when you held 78, then you might re-raise in a similar scenario, because your opponent will often play an Ax suited this way, where the x is the paired board card. For example, say you're in a pot with 78 and the board is 5-6-Q-5. If the river is a 9 and you face a lot of action from a single opponent, you still might want to jam the pot because it's more likely he has trip fives than a full house, because fewer cards on that board are within the playing range. Of course a small pair, like 66 or even 55 is plausible, but many players will limp with an A5s and you can play that hand with confidence, depending of course on your read of the player's post-flop actions. It's a lot tougher to play a straight with confidence if there's a J-J-T on the board. Similarly, you should jam the pot whenever a JT would have a four-straight, even if you have a great hand like top set. In a three-handed pot, don't slowplay a hand like QQ on a flop of Q-9-7, because you don't want to give a JT or a flush draw infinite odds at drawing out on you. You really would like an overcard to fall so someone makes top pair, but the K is a dirty overcard, because it makes the straight possible. If you're going to slowplay, you don't want your payoff cards and the cards that might lose you the pot to be the same. That happens often when someone holds a JT. If you had 99 on a flop of 9-6-2, obviously that's a much better spot to slowplay, because there are a ton of overcards that can fall, but still won't beat you.