Take the Turn or Cross the River   

If you are still in the hand by the time the fourth or fifth community card is dealt, you now have the chance to either increase your winnings or lose more chips.  That being the case, it is imperative that you are cautious about how you play your hand. 

Usually when it comes down to the turn and the river (or Fourth or Fifth Street), there will likely only be 2 players remaining in the pot besides you.  If you still don’t have a straight or a flush, it is foolish to try and stay in the hand unless you are the first player to bet and can check during the Turn.  Nonetheless, it is possible for the final card to grant you a straight or flush, but this is very rare and is a gamble you should refrain from taking if the stakes are high.