A lot of system players argue that it's not the house edge that makes you lose, but the variance -- the wild swings and bad runs.

I concede that IF (and it's a big if) you could reduce the variance, then some kind of progression might work. If it could be reduced enough, then it certainly WOULD work.

Trouble is, the only way to reduce the variance is by increasing the accuracy of your predictions, and since spins are independent, past spins don't indicate future spins. IF you could reliably forecast a series of even money bets such that the longest losing run was 3 or 4, or even 5 or 6, then you could clean up with a simple double-up progression. In my view this is a fantasy; there is no way of reducing the variance to anywhere near such a level.

I'm aware, of course, that one of the ways of reducing volatility in stocks and shares is to spread your risk over a number of markets, but I don't see how this can be applied to roulette. The concept of hedging can't be applied in a random game.