AFAIK, investors are normally willing to invest one hundred now and get one thousand several years later.
Not quite. VC plans on 9 out of 10 deals not working out. So that remaining 1 in 10 has to make enough to pay for the rest. That means that a 10-fold return just breaks even. But it gets worse. For an investment with a 10 year horizon they need to beat alternate investments. If you peg those at 10%/year (compounding annually), then you now need a 25-fold potential return on investment for the fund to have a chance to meet its goals.