But the actual decision was driven in part by a personal experience, Benioff reveals in his new book, "Trailblazer."
He had a vision that Twitter could integrate well into Salesforce's business, becoming a great way for his customers to reach their consumers. A lot of his advisors were against the idea, saying it would be too complicated and risky. He kept pushing forward anyway.
Then, as he was heading to a meeting to begin to secure financing for the deal, Benioff slipped on a curb and sliced his leg open.
He took it as a sign that he should think twice. He recounted the circumstances in a recent phone interview:
"I slipped on the sidewalk and split my leg, and had other problems with my knee," Benioff said. "As I had blood dripping down my leg as I was pitching the bond-rating firms, [I was] thinking to myself, 'Is this a sign?' Maybe I shouldn't be moving in this direction. But I so strongly loved my vision of what it could become. Eventually our investors, who are a key stakeholder of mine, they said no, we don't really want you to move in this direction."
Benioff has been a huge critic of social media company Facebook, comparing it to cigarettes because the platform uses technology to make it hard to quit. He acknowledged that Twitter has similar problems — "Hopefully they're cleaning it up."
He also criticized CEO Jack Dorsey for his refusal to support Proposition C, which imposes a tax on wealthy San Francisco companies to raise more funds for fighting homelessness. (It passed with less than the two-thirds majority necessary to avoid a legal battle, and is now in the courts.)
"Jack Dorsey was quite against Prop C and helping the homeless, even though between Twitter and Square, they've created between 50 and 60 billion dollars of market cap — or maybe more now [Ed: it's actually around $55 billion as of Monday afternoon] — they were not supporting the major homeless NGOs and major homeless programs. They still aren't."
He adds, "When you're in San Francisco, you and I know that if your stakeholder is not the homeless, I don't know who is."