Putting may be my favorite area to teach. It is a skill that is not predicated on size, strength, or speed. While it seems to be the simplest aspect of the game, it gives players fits and frustrations.
I believe those frustrations are caused primarily to an inability to understand why a putt did or did not go in. When a putt is miss-evaluated the player will focus on the wrong aspect of what happened and may try to fix something that is not broken.
To that point it is critical to understand what goes into making a putt and how to evaluate it.
There are 3 major components: start direction, speed control and green reading. The stroke itself only controls start direction and speed control. Green reading is what allows players to pick a good target in which to start the putt.
I have attached a video of putts rolling using the perfect putter from two angles. Pay attention to the putts and see what you notice. The perfect putter does exactly what its name says, it rolls the ball perfectly. In this video every putt started on the exact same line.