A lot of the system sellers like bazza rely on low volume of bets (Av 18 - 35 bets a year ) to drag out the punting torture to its end degree before you go broke.

In saying that though one could call these "Special bets" and perhaps have a much larger stake whilst continuing to use the trusted Wt Ratings.
i.e Barry Watsons excellent mechanical system.

Cheers
darky