Knowledge is powerful. With the right knowledge, we can change the world. With the bad knowledge, we can harm others. In order to get the full power of knowledge, we need to put it all together.
Learning certain facts and letting them get scattered in our minds is not putting all of our knowledge together. If you put all of the knowledge together that you learned in all of the science classes you took, you would have enough knowledge to become a scientist. However, that is not what everyone wants to do in life, and as a result, some of those knowledge gets scattered.
Although you may not want to become a scientist, there is something that you want to do. In addition, you could already have a job that you love. The job you are in or the niche you want to pursue is the area where you need to put all of your knowledge together. It is possible that you work at the same or similar jobs (or stay in your niche) for the rest of your life. You do not want the knowledge you learn to go away. Once you choose what you want to become, you need to focus a good portion of time and energy into what you decide.
In order to become the best in the world at what you do, you need to retain knowledge. By retaining knowledge, you will be able to obtain more knowledge with ease. In school, flash cards are a commonly used resource to remember material. However, writing definitions on flash cards and testing yourself seems beneath the real world. The best way to remember certain things about your niche and retaining your knowledge is by writing things down that you want to remember. I have a notebook with notes about my niche. I occasionally look back at the notebook and look at I wrote down. As a result, I am able to remember all of the important things about my niche that I need to remember. Instead of forgetting about a tactic to get an extra 100 followers every day, I have it written down in my notebook.
If you do not have a notebook, then you need to get one. Although flash cards are not the best study methods for people in the real world (because flash cards are easy to lose and scatter knowledge), keeping all of your knowledge in one notebook will allow you to look back and remind yourself of important facts and methods revolving around your niche.