Notching is all about the angles, nothing else. With the same angle you can more or less know where your shot is going to land if you experienced many 3 sec shots, so you can shoot with the proper power. Same applies to 5 sec LG for instance, but of course these shots require being able to hit the good power and getting the good aim. Knowing what your aim is a big help indeed, but that doesn't mean you will know which aim to use in any given situation. The more you practise the better you get, it's that simple.