Playing in an individual tournament online, I accepted my robot partner's game invitation and found myself in 4H. Follow along with the deal by clicking on the "Next" button.
They take the first two tricks, the second one with a ruff. Then, East leads a diamond to my Ace under which West drops the King. I play the Ace of hearts and East's king drops.
They have misdefended -- East ruffed the club with a natural trump trick. Can I capitalize on their mistake and make the hand now?
I pulled the remaining trump, ending up in my hand and took the spade finesse but it was Too Late Now. I still had a diamond loser.
I can maximize my chances better. If East started with KQ doubleton diamonds, I can play the 8 diamond and duck in dummy. My losing spade goes away on the Jack diamond. And if this doesn't work, I still have the spade finesse available. The point was that with the spade finesse, I still had a diamond loser. So, it doesn't cost to try for this extra chance (made likely by the drop of King diamond under Ace).