Even before WeWork was bailed out, its struggle to go public had caused some of its early investors to write down the value of their holdings. In recent weeks, Goldman Sachs and Jefferies, a smaller investment bank, reduced the value of their stakes in WeWork by about $80 million and $146 million during the third quarter. Both investments remained profitable at the end of the third quarter.

And those who bought shares of some of the most valuable start-ups during later funding rounds are in many cases under water. A 2017 investment in Lyft by the mutual fund giant Fidelity valued the company’s stock at about $47.35, according to EquityZen, a marketplace for private stocks, while Toyota’s investment in rival Uber last year valued that company’s stock at $48.77.

On Friday Lyft’s stock closed at $44.54, while Uber’s ended the day at $32.71.

All of this is fallout from an investment bubble that had formed in the private markets that fund start-ups, as big investors with billions of dollars piled in. Behind this wave of investment was a change in rules on private investments, record low interest rates and a fear of missing out on the next transformational tech company like Google or Amazon.

Fund companies including Fidelity and T. Rowe Price, which had typically invested only in public companies, started taking part in private funding rounds, and so-called mega funds, which could make huge bets on a single firm, most notably SoftBank, were born.

Soon the sums raised in private markets were dwarfing the money from I.P.O.s. Over the past six years, companies have raised about $550 billion from venture capital funds, easily exceeding the $320 billion of proceeds generated from I.P.O.s over that period, according to data from PitchBook and Dealogic.

But the private money meant companies could grow without the scrutiny of public-market investors — no quarterly financial updates or demands for proof that they would find a way to become profitable. Now that they are moving into the glare, it has become evident that a number are still far from being ready to live up to the market’s demands.