Apollo Global Management Inc. co-founder and CEO Marc Rowan said Tuesday that private loans are now the biggest source of opportunity for investors wanting to outperform the markets.

“Active management has failed to beat the index 85% of the time for 20 years,” Rowan said in an appearance on Bloomberg TV. “And I think it’s going to get harder, not easier.”

Rowan said beating public markets is becoming more challenging as they become increasingly interconnected.

“Public markets are so correlated and indexed to interest rates and to money flows, that if you actually want alpha, out-performance, you need to step away from public markets,” Rowan said.

He made the same case in an earnings call November 1, highlighting that the S&P 500 represents 80% of market capitalization and that 10 companies make up 35% of the index.

“These 10 stocks have traded between 52 and 44 P/E [price to earnings ratio] over the last few weeks,” Rowan told investors. “Not many of you come in every day looking to buy 50 P/E stocks.”

Instead, Rowan is championing Apollo’s specialty, private credit. Apollo is one of the world’s largest alternative credit investors, managing $443 billion in credit assets as of Sept 30.

“If you can get paid for illiquidity, why not get paid for illiquidity if you’re a wealthy individual, how many of them need 100% of their money on Tuesday,” Rowan said on Bloomberg. “If they don’t, they should get paid for illiquidity.”

Apollo reported in November that its total assets under management increased by $108 billion to $631 million in the quarter ended Sept. 30, up 21% year-over-year from $523 billion.