In a private letter to clients, Baupost Group CEO Seth Klarman suggests that, instead of asking themselves why they should sell in today’s market, they should ask whether they can afford not to, according to a recent article in Business Insider.

Klarman’s concern, the article says, is that investors are overlooking risks associated with low volatility and stretched valuations, and that “growth stocks—those that represent high quality companies—are appreciating far ahead of value shares, which tend to trade lower than merited.”

In his letter, Klarman reported that Baupost, one of the world’s largest hedge funds with $31 billion, saw almost no profit in the third quarter. According to the article, the firm intends to return “a hefty chunk of capital to investors by year’s end,” adding that in his letter Klarman argued, “whatever edges talented investors normally possess are whittled thin. Sellers become scarce, dislocation infrequent, and the rising tide lifts all boats.”

This is not the first time Klarman has issued a warning to investors, the article says, adding that in client letters from earlier this year he argued that investors’ perceptions of risk were “unreasonably muted.”