As an example to all of this – here’s a bridge hand (quoted originally by Terence Reese)

South arrives in 4S and West leads the K. How do you play the thing?

Well, count your tricks. There are six Spades, two red Aces and a Club. The Heart finesse might succeed or West may hold the A. To take advantage of both of the possibilities for extra tricks South should win trick one (if he ducks, West may be up to finding the killing Heart switch) and must play a Club immediately. Why not draw trumps? Well, let’s see what will happen. After playing three rounds of trumps South leads a Club and West allows dummy’s Q to win. Now what? Declarer is stranded in the dummy. If he comes off the table with a Diamond West can cash two of those before playing a Heart. Thank-you and goodnight. Of course, West might extricate declarer from his misplay by putting his A on the first round of the suit – an egregious play that would prove, once again, that at bridge two blacks definitely make a white.