One of the most important differences between playing no limit Texas holdem poker and playing Texas holdem with a limit is the so-called “trouble hands.” In limit, hands like KJ, KQ, and AT (that's ace-ten) are pretty good hands. If you have one of those hands on the big blind, it's usually correct to call a single raise. If it turns out that the raiser has AK and winds up flopping a better pair than you, you're going to lose some bets, but it won't be a disaster.
In no limit and pot limit Texas holdem, it's a whole different story. Defending your blind with KJ is not always wrong, but you need to tread carefully. Losing your stack every time a K or J comes on the flop and you're up against a better hand is a sure recipe for going broke quickly. At the same time, that need to be cautious means you can be forced to fold the best hand when you're faced with a big raise from a flush draw or even a stone cold bluff. When you're just playing poker for fun with your friends, go ahead and gamble it up, but in a serious game it's usually best to throw these hands away.
