When someone invest 200M at a 1B valuation (for 10% ownership), remember that only the $200M are real at the moment. The rest, $800M, is "confidence in the team + hope in the market." This is especially true when the company makes no revenue.
So in the event the company sells for $300M, the investor get first get his $200M out. Then get 20% of the remainder. He won.