Source: www.vba.asn.au
With no one vulnerable, you pick up the following hand:
and find yourself playing 2
after the following auction:
Dealer: W; Vul: Nil 
The opening lead is 
J. You have two heart losers, one diamond loser and two club losers. To make the contract you will have to avoid a trump loser.
What is your plan to make the contract? How would you tackle trumps?
You can play the king and ace, hoping trumps break 2-2.
Alternatively, you can finesse against the Q with either opponent. Ordinarily, each line would offer about a 50% chance of success.
Before committing to either line, you could “read the opponents’ cards” as such:
Q1) Who has the Q?
A1) East has it because the J lead denied the Q.
Q2) Who has the 
A and K?
A2) It is not clear who has them, however West doesn’t have both the A and K because he would have led one.
Therefore, East has either the A or K or both.
Q3) Who has the 
A and K?
A3) For the same reasons as above, East has one or both of the A and K.
Q4) What is East’s range of high-card points?
A4) The 1NT response (Standard American) promised between 6 and 9 HCP.
Conclusion: East’s high cards include the Q, only one of the A and K and only one of the A and K. Another high heart or club would give East at least 12 HCP, too many to respond 1NT and leaving West with a hand not good enough to open. Similarly, East also can’t have the Q or Q as she would then have at least 10 HCP, also too strong to respond 1NT. West must have both the Q and Q.
The full hand: