North leads the 
A, followed by the 6 to South’s king. South continues with the J and you discard the 
7 as North discards the 6. South now plays the A, which you ruff, North playing the 10. You cash the 
A, K, all following and South playing 9, Q. How should you proceed?
TWO PAID OFF OR 2
OFF
Without due care it is easy enough to take your eye off the ball when you are in a low-level contract. This arose in a National Swiss Teams: 
It is a simple matter now to play a third club at trick seven and ruff with the A, ruff a heart low and ruff a fourth club with the J. Even when this is over-ruffed, you score five spades in hand, one in dummy and two club tricks.
Although the Q is likely to be with North on the bidding, you do not to need risk ruffing the third club with the J. If you do a nasty surprise follows. South over-ruffs and plays a fourth diamond. You can ruff high, but when North sheds the K, you are limited to four trump tricks in your own hand and will be one down.