I ran the Barcelona simulator and it was a bad result
<insert surprised Pikachu face here>
It takes two flops at 1.2 odds to to boost your required bet from 10$ to $500, add two more 1.3 and you're down $5k for $10.
If you apply this on sports betting, say, you place a $20-bet on Barcelona and you lose. You double on your next bet and you win. It doesn't mean you recovered your $20 loss. It may happen that you won on a 1.20 bet, meaning you only won $8 from your $40 bet, which further means you still have a net loss of $12.
That's why you need to increase the bet, what you're playing is not Martingale, you simply "flat betting" using the same amount.
For a 1.5 you need to double, for a 1.25 you need to quadruple, and this will soon spiral out of control, especially with a favorite.
Look how this scenario turned out:
Good old gambler fallacy and why martingale is a bad idea!