Frequently a player will win a trick with a card that he/she clearly did not count on to win a trick. For example winning with a jack of Clubs when Spades are trump. In certain situations this should be a "heads-up" for you. For example if the player only bid 1 trick then he/she is probably still holding a high trump or Wizard card which must be unloaded. You can often use this information to your advantage or you may simply need to adjust your play accordingly.