It might be their first time on that route/ride also. What happens is they are bombing along down a good hill on their highest gear or in tuck/coast trying to hit maximum speed. Suddenly, it changes into a climb in the 6-10% range. There is no runout before the climb. Or, there is a blind turn coming up. The rider goes to the brakes hard, makes the turn, and encounters the same sudden 6-10% climb. Over and over again.