The loser count is one too high
Phyllis Diller said, "Aim high, and you won't shoot your foot off."
In many bridge deals played with a trump suit, declarer finds that his loser count is too high. He must find some way to eliminate those he cannot afford. Two common ways of doing that are ruffing a loser in the shorter trump hand, or discarding a loser on a side-suit winner in the other hand. In this deal, though, South must find a different method. How should he play in four hearts after West leads the spade queen?
South could see one loser in each suit. He had just nine winners: two spades, five hearts, one diamond and one club. The only realistic chance for a 10th winner was to find East with the diamond king. But that would require two dummy entries: the first to lead toward declarer's diamond queen, the second to reach the diamond ace after unblocking the diamond queen. Where are those two entries?
They must both come in the trump suit, so South has to be careful with his heart three.
After taking the first trick, declarer leads a middle heart to dummy's 10 (or queen). Suppose that East wins and returns a spade. South takes that also, plays another middle heart to dummy's queen (or 10) and leads a diamond toward his queen. East goes up with his king and plays a third spade. West wins and exits with a club. Declarer takes that trick, cashes the diamond queen, overtakes his heart three with dummy's four and discards his club loser on the diamond ace.
It was a lucky contract, needing the diamond king onside and hearts 2-2.