For example, you can readily use your own life's experiences to make a judgment about how likely you are to drown in the tub, or to be killed by lightning, or to die from cancer from drinking a lite beer a day for a year, eating char-broiled steak once a week, or eating peanut butter sandwiches daily. So when you see these figures (or ones you choose) on the scale, you get an idea for how likely other risks in that zone are.