English philosopher Thomas Hobbes said, "Science is the knowledge of consequences, and dependence of one fact upon another."
    Sometimes during a bridge deal you will be faced with an apparent guess. Should you bid one more or not? Should you duck a trick or win it? In the bidding, make a mental list of the possibilities and analyze each. With luck, it will become clear which call is best.
    In the play, consider your options, their consequences, and whether your decision fits the facts.
    Look at the East and North hands. You, East, are defending against four hearts. West leads the spade nine. How would you plan the defense? In particular, would you win the first trick? If not, which spade would you play?
    You know that partner has led a singleton or top of a doubleton. If it is a singleton, you must win the first trick and give him a ruff. But if he has a doubleton, you must duck this trick, signaling enthusiastically with your eight to encourage partner to continue spades when next he is on lead.
    What is the consequence of partner's having a singleton spade? That would leave South with five spades. Would he have opened one heart with five spades in his hand? Only very rarely, when he had a strong hand with five spades and six or more hearts. You should discount that possibility.
    So partner has led from a doubleton. You must not win trick one.
    West will get in with his heart king, play his second spade to your ace, receive a spade ruff, and cash the diamond ace to defeat the contract.