Roizen believes that in the VC business, most companies fail. Therefore, the rare successes of their portfolio companies has to be big. Often you hear 10X, i.e. you should see 10 times your capital coming back, she says. It is also calculated as dollars in, dollars out, or internaI rate of return (IRR). The Mobius fund today has an IRR of 90%. Roizen notes you will almost never hear a VC use IRR.