Source: ACBL
As I’ve illustrated:
[box]You shouldn’t try to bid every slam that just happens to make.[/box]
You should never play partner for the perfect hand. If you do, it is likely that the only time you will see a perfect dummy is when you look in the mirror!
Given each of the following auction situations, a good slam is very rare. Infrequently you might be able to bid six and feel confident that your hands justify the bidding. But as a general rule, given the conditions that follow
— regardless of whether you are advanced, intermediate, or newcomer
— I strongly recommend that you don’t push for slam!
Situation 1: When partner opens at the one level and your right-hand opponent makes a takeout double. I am aware that some players double with marginal hands. While you might have 12 tricks, it’s too hard to bid, even for experts.
Neither side is vulnerable and you hold: 
K10 
AK8 
KJ74 
QJ43
Content yourself with bidding 4.
Keep in mind that an opponent’s take-out double is often based on shortness in opener’s suit. A bad heart split will greatly reduce partner’s chances of making six .
Situation 2: After an opponent opens the bidding at the one level in first or second seat. The logic here is very similar to situation 1. It’s true that more and more players open light these days. Despite that, slam is still unlikely after an opponent opens. On those rare occasions when you can make a slam, no partnership is well equipped to get there.
At favorable vulnerability, you hold: QJ102 AJ6 KQJ7 AK
Pass, despite your 21 high-card points. Partner can’t have much. The other three players have a total of 19 HCP, and East did open. At this vulnerability, any time partner is short in hearts, he will be eager to sacrifice by bidding 4 over 4.
Situation 3: When you are a passed hand, slam is very unlikely. The only two exceptions are when partner opens 2, and when partner opens one of a suit, you find at least a nine-card fit and at least one of you
has excellent distribution.
For example, you pass in first or second seat holding: KJ3 KQJ Q54 7543. Partner opens 2NT.
Bid 3NT. You correctly passed originally because your hand was extremely unattractive. Once you subtract for 4-3-3-3 distribution and too many quacks (queens and jacks), this mess is not worth 12 HCP. If partner had opened 2 and rebid 2NT, then you would have been interested.
Situation 4: When partner opens and you respond 1NT, slam is rare unless opener jump shifts and you have a nice fit in his second suit. This is true whether or not the 1NT bid is forcing. The auction proceeds 1-1NT (forcing); 3 and your hand is: 6 A87 KQ9 Q87532
Bid 3NT. Obviously, you could have had much less for your forcing 1NT response, but without a fit, you should be content to play in game.
Situation 5: When responder makes a limit raise, opener should consider slam only when he has both a terrific hand and a singleton or void. You open 1 and partner bids 3 showing a limit raise with four-card support.
Holding: KQJ986 AQ QJ4 K3, bid 4. Slam is very unlikely. You have only one ace, and the majority of your honor cards are quacks.