Like many of the lessons taught in driver-education classes in days of yore, the exhortation to "pump the brakes" when skidding on a slick or snowy road wasn't entirely correct. The problem that this technique was supposed to address was brake lockup. Although it may seem counterintuitive, a locked wheel, i.e. a wheel that isn't turning, doesn't stop nearly as effectively as one that's turning slowly. Also, if the tires are skidding, you lose all directional control, which means that you can no longer can steer the car. So Job One, when confronted with locked wheels, is to release the brake to allow the tires to start turning again. Only then do you reapply the brake. Although this sounds vaguely like pumping the brakes, the technique is far more subtle and requires a much more delicate touch.