Sentence:  As an example: if a player is well ahead, and sees the opportunity to gain a <WSD>rubicon</WSD>, he should discard cautiously and play so as to prevent his opponent from saving the <WSD>rubicon</WSD> by scoring 100 points. 
Meaning of the word marked with <WSD> tags:  Especially in bezique and piquet: a score which, if not achieved by a losing player, increases the player's penalty.