Eugene Zhang, founding partner of Silicon Valley VC firm TSVC, recalls the exact moment the market for young startups peaked this year. The red-hot market suddenly cooled, with investors dropping out in the middle of funding rounds, leaving founders high and dry. As the balance of power in the startup world shifts back to those holding the purse strings, the industry has settled on a new math that founders need to accept, according to Zhang and others. The painful adjustment rippling though Silicon Valley is a lesson in how much luck and timing can affect the life of a startup — and the wealth of founders. More private U.S. companies hit at least $1 billion in valuation last year than in the previous half-decade combined. . . .