Your life total is higher than or equal to an opponent's.
Steps
Activate Diamond Valley by tapping it and sacrificing Soul of Eternity, causing you to gain life equal to Soul of Eternity's power.
Sanguine Bond triggers, causing target opponent whose lifetotal is less than or equal to Soul of Eternity's power to lose life equal to the life you gained.
The opponent loses the game due to having zero or less life.