Declarer was unlucky to go down, as the contract would make if the diamond finesse was on, or if trumps divided 2-2. The contract however could have been guaranteed by relying on solid technique rather than luck. Did you spot declarer's fatal error? Declarer dug his own grave by drawing the second round of trump. The safest play is to cash the ♦A, ♣A, concede a diamond, win the likely trump return and crossruff the hand. Since the North and South hands contain all the high trumps, this line of play guarantees the contract.

The above line of play gives up the chance to make an overtrick. An alternate line of play would be to take the diamond finesse after playing one round of trump. If the diamond finesse loses and another trump comes back, declarer is in control; he wins the trump return, cashes the ♦A, ruffs a diamond in dummy, cashes the ♣A, ruffs a club in hand, and ruffs the last diamond in dummy for the tenth trick. This line of play however risks the contract if diamonds divide 6-1 (which is extremely unlikely), in which case the defense may be able to engineer a diamond ruff.

Choosing either line of play is reasonable. The point of this deal is not to draw trumps prematurely when side suit losers need to be dealt with.

Analysis:
Bridge Baron 17's double dummy solver confirms that if declarer draws two rounds of trumps, the contract cannot be made from that point.

Bridge Baron's Line of Play:
Bridge Baron decided to give up the overtrick and chose line 1 and cashed the side suit aces, conceded a diamond and crossruffed the hand for 10 tricks.
Par Contract Analysis:
The par contract on this deal is 4♥.

Bridge Baron deal No : N4446-37542-83504-67668-21096-33145