Unlike those of other sports, our playing field is neither flat nor standardized—and therein lay its charms. Uncertainties lurk around every turn and test your versatility and preparedness. Vigilance is rewarded with thrilling sensations, but get caught unawares, and you’re bound to go down. Nowhere is that more true than on a rollover or drop-off, where a slope steepens abruptly. You get a little jolt of adrenaline as the ground drops out from under you and your skis take flight. You’d better keep up with them, or be ready for a crash landing.