Stephen Schwarzman built Blackstone into a $1.3 trillion firm and never made it past basic math. The man who runs the largest alternative asset manager on Earth says finance is not about numbers. He's right. The proof is in his single most profitable trade. In July 2007, Blackstone bought Hilton for $26 billion at the absolute peak of the credit cycle. Twelve months later, Lehman collapsed. Hotel occupancy fell off a cliff. The mark-to-market on the deal turned brutal. Every model on Wall…