Recently i played in a tournament on PokerStars and one (good) player said to another after the hand:
"Don't bet at the river if u don't want to call an all-in.." I never heard about such a "rule" or "guideline" - what´s your opinion on this ? 
Sounds like one player made a value bet on the river and the other player shoved, at which point the first player folded.
No, there's no such "rule." In NL HE, though, generally you don't bet a large portion of your stack on the river only to fold to a shove, leaving you with a very short stack. (The better move is to shove yourself if you are willing to go all in. Or check, perhaps to induce a
bluff against your good hand. But it all depends on how the hand has played out and what you have and whether the other person could have you beat. It also may matter if it's the bubble.)
There are many schools of thought on this, and players disagree a lot. Some (me) believe in living to keep playing in a tournament -- a short stack can come back but a busted player is just done. Why go bust when you feel sure you are beat?
That flopped straight just doesn't look that good when the other guy could have made a flush or a boat on the river but you don't necessarily want to check.
