Eric Rodwell's classic book, the Rodwell Files, is loaded with advice for advanced-to-expert players. I have taken the liberty of slightly modifying a deal from his book as follows:
South holds:
-- 
AKQJ1073
A53 
KQ8.
With neither side vulnerable, East opens 3. South decides he is too strong for a 4 overcall. He starts with double and is less than thrilled when his partner removes to 4 (no big surprise that partner bid spades!). Anyway, North must have some values, so South jumps to 6 and buys it there. Thank goodness partner doesn't correct to 6! The 6 is led and South sees:
| KQJ32 42 742 A109 |
| -- AKQJ1073 A53 KQ8 |
South has two diamond losers. The only source of discards is dummy's spades. There are entry issues to consider.
Declarer wins the lead and draws trump (they are 4-0). East discards two diamonds and two spades. Now what?
Will you finesse West for the J? If so, you can lead the 8 to dummy's 9 and if it wins, lead the K for a ruffing finesse. East, who is marked with the KQJ1098 won't also have the A (he preempted). From the bidding and lead, you know West had a singleton diamond. You can throw a diamond on the K and later get back to the A to throw another diamond on the spades. Is that a good plan? No, for two reasons. One, a clever West player can thwart your plan if on the first round of clubs, he inserts the J. That means only one dummy entry and no chance. And two, take a look at the full deal:
| Vul:N-S Dlr: East |
KQJ32 42 742 A109 |
|
| A10954 9865 6 654 |
876 -- KQJ1098 J732 |
|
| -- AKQJ1073 A53 KQ8 |
As you can see, East has the J--a clubf finesse results in down two.
Assuming that West held a singleton diamond and the A, there was a 100% line of play available. It didn't matter who had the J. After drawing trump, declarer makes the brilliant move of leading the king of clubs and overtaking with dummy's ace!
Now comes the K, throwing a diamond. West wins, but that's all the defense gets. Whether West plays another spade or a club, declarer gains access to the dummy and has 12 tricks.