When you bet on martingale, it is normal that you may not realize 19 times in a row win as well. If you bet on 10 satoshi per bet, you are going to win 190 satoshi when you go 19 wins in a row, not really a ton of money right? But, when you lose 19 times in a row and start at 10 satoshi and double it every time you gamble you are going to end up at 5,242,880 satoshi or better yet 0.52420880 bitcoins, that is over half a bitcoin at the last bet and of course a ton more until you reach there, almost one bitcoin lost, and you only try to win 10 satoshi when you recover it all. So, it is understandable that you may not realize 190 satoshi won thanks to 19 wins in a row, but it is also easy to calculate 1 bitcoin loss when you go 19 losses in a row.
No, it is not rare to have 19 times losing streak in a dice, others even goes up more than 30x in a row. And btw 5,242,889 is just 0.05242889 BTC not half of Bitcoin since 1 BTC is equivalent to 100 million satoshi.
Though martingale is a devastating strategy when a consecutive losing streak happens, but 1 win after long losing streak can easily gain what you lost plus some winnings depending on how much is the multiplier you set up on it.