Concentration

I realized that I only can focus on several thing at once.

For very short term, like less than 10 second, It's hard to hold one thing and be productive at other activity. For example, watching movie and have meal at same time, or hold a things to do while study. Or, study when you in hunger.

Writing down or do easier work is solution.

For long term, maybe more than a week, the activity should less than 3 or 4. For example, in my case, I only study this moment, but anything. I'm currently working on Python for software engineering, CCNA for network managing, and some game. The activity should remind myself in regular basis and this cannot be done when there is too many things to do.

So this is why I don't buy another course in Udemy. There is only one paid course, which is CCNA. I can buy another one, but I can't concentrate on different thing at the same time.