In Gin-Rummy, when not to Knock?
From Rummy-Talk: When to Knock, Play for Gin, or Underknock


  Knock, under most conditions, should be utilized at the first opportunity, with a few
  exceptions:
  
  
  When the odds are in favor of your going out in a game, or obtaining
  enough score to catch up to your opponent. 
  When it is a reasonable
  assumption on your part that you stand to be underknocked by laying
  off his cards. 
  When you know that your opponent is not in a position
  to knock his hand 
  When you have your opponent’s hand dead. 
  When your hand has the characteristics of a gin hand.