Teacher and student

 Even if the best teacher teaches, or no matter how good the teacher's teaching is, not all who have been taught can achieve good results. Of course, it is clear that having been taught by a good teacher increases the chances of getting good results, but the outcome will depend on how well the person who is taught understands and practices the teaching well with will and effort.

 For example, if someone knows the presence of a Buddha and has seen his teachings, it doesn't automatically bring them good results. Or just being close to an excellent math teacher and watching him solve a difficult math problem doesn't lead to automatically becoming good at math. Only when we understand teachings and consistently practice them, there will be possibilities for good results.