If your goal is to gain 20% per month with a high-probability Martingale-style strategy, your chances are improved by just making a single bet at 1.2x profit each month with the entire capital. The higher the probability you set in your strategy, the less likely it is to hit a losing streak long enough to break your bank, but the more runs you need to do to achieve the same profit, offsetting the reduced chance to lose.
You can run the numbers and see this quite clearly, but there's also an intuitive way to think about it. JD takes, on average, 1% of the amount you bet. If you make a single bet, you have an expected 1% loss on the amount wagered. If you use a Martingale-style strategy, you bet the same money more than once. To achieve, say, 20% profit, your total amount wagered will be more with a Martingale-style strategy than with a single 1.2x profit bet. And since in the long run, you expect your losses to reach 1% of the total amount wagered, the Martingale-style strategy loses. (the 20% profit is an example, it holds true for other values as well)
tldr: Dabs, if you set a monthly profit goal, I can outperform your strategy by placing a single bet each month (if I had magic beans, special seeds, dragons and all the yada yada of course).
I tried explaining this to him for a very long time..
It won't work. He's a persistent bugger, he's having fun though, so fair enough.