> Problem is flipping the coin 20 times. I don’t think even 1 in 100 million would do that.

2^20 = 1048576

So roughly 1 in 1 million.

You're off by 100x.

I believe OP is talking about the human emotion of flipping that coin the 19th time (or indeed the 18th, or 17th...). While the math might be as simple as doubling x times it's very different to actually do it!

Are you forced to bet everything on every flip?

If your goal is to double your money on each successful flip (as implied in [0]), then yes.

[0] https://news.ycombinator.com/item?id=37586995

I think that's the implication: https://en.wikipedia.org/wiki/St._Petersburg_paradox https://en.wikipedia.org/wiki/Martingale_(betting_system)

That's where skill comes in and invalidates the point that it's all luck.