Its just retarded.
No...
Investing 1 btc to win 0.5 btc with a 70 % chance is not retarded.
Expected Value = 0.7 x 0.5 + 0.3 x (-1) = + 0.05
And with a correct martingale, and a good money management you can even optimize the probably and equity to win.
Nonsense. You do not haven 70% chance of winning 0.5btc by risking 1btc using Martingale. If that BS was true, all Casinos in the world would be broke.
Let's say OP wants to win 0.02btc playing Martingale.
He only has 10.22btc, so he HAS to stop at the 9th loss in a row.
Losing 9 time in a row is pretty common stuff (I'd say a serious Martingale player should be ready to go to +15 bets). If OP is ready to double his bets every time he loses for 9 times, he is risking 10.22btc to win 0.02btc. Yes, he will win most of the times - but when he loses that loss (10.22btc) is stupidly huge compared to the potential win (0.02btc).
Last but not least, the point is that if he plays long enough, he will always lose.
-EV games (gambling) are pure and simply retarded.