I was curious about the potential for returns so I considered a scenario: the successful YC companies take series A investment at an average $10 mm pre-money valuation (which is reasonable for a YC company starting off with $150k), and no series B is ever needed before exit. This gives the original investors a 1.5% stake at the time of exit.

In order to return the $6 mm there needs to be $400 mm of exits.

But I don't think it's reasonable to assume that the successful companies wouldn't take additional funding past series A. More likely, any successful company would also take series B funding. Then we'd need to see ~$500 mm - $800 mm to break even.

My guess is that these investments aren't really intended to be profitable. I would guess that they're instead a gateway into future deals that will be profitable.