In early October, WeWork’s board of directors trickled into a brick building in lower Manhattan where the startup had an office. After they took their seats around the conference room table, Mark Schwartz started to vent.

“I’ve stayed silent too long,” the 65-year-old former Goldman Sachs Group Inc. partner told the six other men on the board, including WeWork’s co-founder and chairman, Adam Neumann.

Mr. Schwartz aired his frustrations about the state of the company, which was perilously low on cash after years of freewheeling spending and had become the butt of jokes on Wall Street, according to people familiar with the meeting.

No more fantasies, he said, as advisers and others looked on. Now, he said, they needed to make decisions that would save the company.

Even more remarkable than the content of Mr. Schwartz’s blistering rebuke was the fact that it came so late. The banker had stayed silent so long that the story was almost over.