Bridge by Frank Stewart
West leads the queen of clubs. You take dummy's ace. How do you play?
Your goal is to make the contract. Since you can afford one trump loser but not two, you play safe by leading a trump to your ace. If East-West followed low, you would go back to dummy and lead a second trump. When West's king actually falls, you can pick up East's jack and take 13 tricks. Well done!
Now say the game is matchpoint duplicate, where the goal is not (necessarily) to make the contract but to beat the other pairs who hold your cards. Overtricks and undertricks may be significant.
Lead a trump to your ace again, your best play for 12 tricks. You don't need plus 1,010 for a good result; plus 980 should be enough. (As the cards lie, you'll be plus 1,010 after all.) Evaluating your contract and judging how many tricks to try for are factors that make duplicate a special challenge.