You are end up four spades with silent opponents. Partner splintered your one spade opening with four diamonds. The opening lead is the ace of diamonds.
Dummy
Lead: 
You
You count your losers: perhaps one spade if they break 3-0, one heart, one diamond and no clubs. But do you have enough trumps in dummy to ruff two diamonds and two hearts? Assuming spades break 2-1, how can you insure 11 tricks ?