Basically the way you have to look at martingale is to see each stake size as seperate bet sample. So the 1 unit stake will have most bets and the amount of bets will go down for each stake size. As long as all the 1 unit Bets / 2 unit bets / ... themselves are not +EV you will lose eventually. It's the classic gamblers fallacy and one of the hardest things to mentally get passed as a bettor. Previous results don't have an influence on future results. if it has been 'odds' 15 times in a row, the chance of the 16th tilme being odds again is 50%. it's as simple as that. These martingale strategies pretty much come down to having 99% to win at 1.009 odds you can win for a while and will then lose it all and more with 1 bet eventually.
If anything, I would say do try it out with small stakes, you will likely learn a great lesson which is worth the losses. Good Luck !
Well when I tried and played with my fater we run as high as +1000 E from basic 20 stake. Maybe we got luck. When I try alone I can easily miss 5 in a row. I know probability is always the same, but there is one when I connect 2-3 parlay bets on great favorites with like 1.40 - 1.50 odds. From 5 times they should play as I want or to win once from 5 times X where clubs are close to each other. I tried with X and miserable failed.