This fullness leads to frustration and makes you throw lessons (or, worse yet, quit lessons guitar). Second, only one 'New knowledge' does not lead to mastery. Comes to me a lot of students who can do cool things on the guitar. For example, they may have good technique, or a good understanding of music theory, or a good ear. But more often of their ability to apply and integrate knowledge at a very low level. In this case, 'new knowledge' does not help these students make substantial progress in guitar playing. Just 'know' the principles of game enough. In fact, you do not 'know' something up until you can not apply this knowledge and integrate them with other skills on the fly.
This practice – the use and integration of acquired knowledge, is perhaps the most important thing from those that you get to music lessons, and, thus, an area of musical development, which is almost entirely absent from many players. The absence of such a practice leads to an enormous disappointment, and many guitarists often have it (but often do not understand why they're frustrated). When you take your first lessons, you may think it's great if the teacher at each lesson shows you something new. But if your teacher does nothing, except that the 'show pieces', then eventually you start to notice that you do not actually make substantial gains (because it does not work on the application and integration of the obtained knowledge). Many people drop out of classes at this stage, and contribute to the maintenance of myths about the ineffectiveness of guitar lessons, not knowing the real reasons for the lack of progress.