The top CEO in private equity has a rule for investing ? and it has generated billions in returns

The Blackstone Group has a stellar track record.

The firm now manages manages more than $300 billion in total assets, while chief executive and cofounder Steven Schwarzman has a net worth of more than $11 billion.

It's not financial engineering or dealmaking wunderkinds that have Blackstone's returns outpacing most of its competitors, according to Schwarzman.

Rather, it's a straightforward approach to deals.

"I've learned that all investments have risk," Schwarzman told Business Insider. "One of the rules I've learned is that struggling to try and think your way into making an investment is usually the best way to not have a great outcome."

He continued: "The best investments are the easiest ones to approve. Ironically, when a bunch of very smart people are sitting around a table for hours trying to figure out whether they should do something, that tends to not necessarily lead to the best results."

" The investments where people walk in and the sense is, 'well, this looks absolutely terrific, let's do it,' those investments are almost always quite successful."

That approach seems to have paid off.