The attempt by mutual funds to beat benchmarks by investing heavily in unicorns—private companies worth more than $1 billion—has been disappointing as “newly public companies are being forced to mark down their holdings of private companies that are no longer investor darlings.” This according to a recent article in The Wall Street Journal.

The article reports: “The collapse of the initial public offering of WeWork parent We Co. and the steep decline of Uber Technologies Inc. shares and other recent IPOs have backfired on funds that hoped big stock gains would give them market-beating performances.”

A recent survey by accounting firm Deloitte & Touche shows that about six out of 10 mutual-fund companies hold private shares in their portfolios, up from about three in 10 five years ago. When private share valuations were rising, the article explains, funds marked up their holdings, but some valuations turned out to be overly optimistic. It cites the example of We shares, which were valued at $102 a share in July of 2018, only to drop to below $55 a share before it pulled its IPO last month.

According to the article, “Active fund managers have embraced private companies to boost returns and differentiate themselves from index funds, which are raking in the bulk of investor cash.”