The biggest eye opener for me since using AimPoint's green reading system is just how often putts will double break. But the good news is that I was also surprised that many times you can simply aim the putter at the cup as well to have the correct 'aim point' to make the putt.
Below is a video showing the 'zero line.' Zero line is not exactly the 'fall line.'
There zero line is anytime the golfer has a putt where the read calls for them to aim at the middle of the cup. More often than not, the putt will double break.
So the AIM is at the cup, but the ball's roll will break.
When I did my first AimPoint clinic under John Graham (www.johngrahamgolf.com), we had a putt on the zero line from about 25 feet away. The putter face had to be aimed at the cup, but the putt eventually would break about 3 feet to the right and then come back 3 feet left.
Understanding AimPoint will get you to see those double breaks, understand how they work and how to make them.