People who have extra money or big bank balance might be able to sustain it, else for smaller players martingale might not be an option. One should be able to chart out how many loses in a straight streak they can manage and play and will they be able to sustain even if 10 straight loses or say more for that matter. This would depend on everyone and amount and risk they are ready to take it.
Martingale can only be a personal choice to be honest because even having a big bank roll would not be useful if we are bad at risk management.
Most of the times when we are facing a negative streak in martingale the risk reward ratio goes negative.
Which means we are betting a huge amount but in return our reward will be very less. It would sometimes be absolute foolishness to place such a bet.
Which is why having a proper strategy along with martingale and a good risk management will only help a person to have a sustainable growth.
Proper money management, the very important tool to keep you safe from your gambling activities.
Like what you have said, there's no assurance using martingale the losing streak is unpredictable, most of the time frutrations hits
you up and leads you up to make wrong decisions, you'll find yourself losing control and lose every single cents of your bankroll.
The one who understand risk and have a good setup plan mostly exit the house with a decent earnings.
I wouldn't say losing streaks are totally unpredictable : in fact the more you play, the more likely you'll encounter a long streak. If you roll the dice 100 times you're less likely to encounter a losing streak above 10 than if you roll it 1 million times. Players should be careful about that.