There is a reason why we prefer the “systematic”. It brings us a sense of safety and a sense of grasping the knowledge. When we were at school, our teachers would teach us to “systematically” learn something. In the library or Wikipedia, the documents are formed in a systematic way. So when we manage our own knowledge, we would like to use a similar organized method to categorize it. But such categories are built based on the knowledge that already exists in an area. For example, if a textbook author is a master in a certain area, he may write a textbook based on a framework because his knowledge of the area gives him the ability to build a system. As a learner, the way you manage your knowledge is naturally different from the way a textbook is compiled by a master. You may collect a few chunks here, and some chunks there. Later, you may form the network of this area. I remember when I was a kid, my teacher called the excerpt notebook “collecting honey”. If we are learning knowledge from different areas, we need to actively connect the dots. These are something that we don't expect when we try to build a “system”.