SAN FRANCISCO — The conventional wisdom in the world of Silicon Valley start-ups has been that the founders call the shots and that the investors are cheerleaders — and sometimes enablers — of the entrepreneurs they backed.

But on Tuesday, when investors pressured Travis Kalanick to step down as the chief executive of Uber, the start-up universe was abruptly reminded that investors can flex their muscles and that founders are not untouchable.

“The examples people cite of founders having all of the power are exceptions,” said Lenny Mendonca, a senior partner emeritus at the consulting firm McKinsey. “If investors are worried about returns, they engage. They take control. And that’s what happened at Uber.”

The balance of power at young tech companies has long been a delicate issue. Silicon Valley’s start-up ecosystem relies on founders’ and investors’ getting along — the entrepreneurs come up with the ideas and need the financiers’ money while the financiers need the founders to help them strike it rich. Over time, who holds the upper hand has shifted back and forth.