Source: Mr. Bridge
When you have a suit such as:
Rather than taking your A-K-Q quickly and hoping for a 3-3 break, it will often be more profitable to disguise your strength by leaving the suit until later. This will leave the defenders unaware of your holding and might cause the defenders to discard a club, allowing you to make your fourth trick even when the clubs break unevenly.
South opens 1NT, North raises to 3NT and West leads the 
Q.
You have eight top tricks and your main chance for an extra trick will be from a 3-3 break in clubs. You also have a chance in spades, but the opening lead does not augur well for that. Do not go straight for your club suit; give the defenders a chance to go wrong. Duck the spade lead, win the second spade with the ace, take your 4K and then play a fourth spade. Seems crazy, but what you are doing is making life very difficult for East. 
You can see East’s hand: he has to make three or four discards. If ever you find yourself playing against a defender who does not discard one club on this hand, then you are probably playing against a mind-reader or a player who can see through the cards. 95% of defenders will surely discard a club and that will give you your ninth trick.
The effect of disguising your strength is powerful. Clearly, if you had played the A-K-Q, East would have held on to his +10 and you would probably have made only eight tricks.
When you are playing cards, whether as defender or declarer, it can be easy to underestimate the value of surprise. It is difficult to remember that your opponents cannot see your cards. It might seem obvious to you for East to hold on to clubs, but as long as you do not tell the defenders about your strong suit, it can be very difficult indeed. Conceal your strength in the hope of favourable discards.