Just calculate simply, if I double 40, I lose. 40 becomes 72, but the previous ones are 5 + 10 + 20 = 35. In the fourth doubling, with 40, I earn 32, yet still lose.

There is an idea: if you make event contracts, first invest 10u, if you lose, then invest 20u the second time, if you lose again, invest 40u. This way, the amount you invest each time is the total of your previous losses, until you win. As long as you win once, you immediately stop. Can you always make a profit this way? However, from the perspective of mathematical expectation, assuming a 50% win rate, you will still overall lose. Can someone explain this?
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