You've read it here before: Slam are based on controls (Aces and Kings) and tricks (good, long suits). Today, August 12, 2018 at the La Jolla Unit Game had two examples.
Kent Hartman, my Sunday partner, and I have a tradition when we play: We have at least one auction that is not duplicated anywhere else in the room. Board #9 was the one. Kent opened 1♣ (which, since we play a Weak NT system, means he EITHER has an unbalanced hand with five or more clubs OR he has 15 or more HCP—as any balanced 12-14 HCP he would have opened 1NT). RHO bid 2♦. (He explained later that he thought he was third hand after two passes.) I was looking at: ♠A9753 ♥KJ102 ♦AQ ♣A6 and got quite excited. I bid 2♠. Kent bid 3♣. I bid 3♥. Kent bid 3♠ (not wanting to bypass 3NT). I am sort of stuck for a bid at this point, so I simply bid 6NT. Kent thought a LONG time (about bidding 7NT) but finally passed. His hand: ♠106 ♥A ♦K94 ♣KQJ9732. 7NT is frigid. However, no one got to the grand slam. The board was played 14 times: 8 pairs were in 6NT; 3 pairs were in 6♣; 3 pairs were in 3NT. A more “normal” auction would have been opponents passing throughout: 1♣/1♠/3♣/3♥/3NT/4♣ (now Minorwood for clubs since we have bypassed 3NT)/4NT [two Key Cards with the Queen)/5♦ (asking for Kings)/6♦ (specific Kings—showing the ♦K and denying heart and spade Kings). Even if partner has ♦Kxx of diamonds—which is NOT guaranteed on this auction—he could easily be short in diamonds—the West hand can only count 12 trick——6 clubs; one spade; two hearts; three diamonds. If the diamond King is singleton or doubleton, we only have 11 tricks. So 6NT will be the stopping point.
Board #31 featured a classic “Source of Tricks” suit. West held ♠A74 ♥3 ♦AKQ107652 ♣Q and opened 1♦. Partner bid 2♣ (game forcing). I rebid 2♦. Partner bid 2♥. I bid 2♠ (temporizing, seeking more information) and partner bid 2NT—making my ♠A74 look a LOT better. I then bid 4♣. As suggested by Eddie Kantar, my partners and I agree that any jump to 4♣ over a 1NT or 2NT bid is Gerber—even if clubs have been bid in the auction. Partner showed one Ace—presumably the ♣A. I am expecting the ♠K for the 2NT bid, and I think the ♣K is highly likely which gives me a parking spot for the third spade in my hand. Partner's hearts do NOT, however, have to include the ♠K, and I am pretty sure he does not have the ♥A, so I am not risking 6NT. I bid the sane 6♦ contract which is icy cold. Two pairs were in 6NT getting an undeserved tie-for-top board when ♥A and ♥K were split between the defenders, so declarer did NOT lose two heart tricks off the top. Partner's hand was: ♠K10 ♥QJ109 ♦J9 ♣AKJ103. One pair, obviously with a bidding misunderstanding, bid 7♦ and the opening leader cashed the ♥A for down one. Two pairs were in 5♦. Five pairs were in 3NT and four pairs (including us) bid 6♦.