Work on skills that boil down to written document

There are a lot of different skills in the world such as mathematics, speaking, playing instruments, programming, and so on. Most of them go away if you don't practice continuously. But there are skills that can be saved as 5~10 written documents. In these skills, if you just repeat the steps written in the document, you can do this perfectly fine even after long passage of time. This includes command lines to launch web application (my previous entry on Sunday, March 4, 2018), astronomy (also my previous entry on Sunday, May 24, 2020), and cooking (i.e. cooking recipe). Using these documents I am confident that I will be able to do these well in 20 years. For example, the commands for launching web application were already used to launch three servers that helped hundreds of people and many more. It is nearly impossible to practice one skill continuously for the rest of your life.  

Skills that cannot be written perish. Skills that can be written accumulate.