I almost always only learn things that I can immediately apply afterwards, because otherwise I find I don't retain enough useful knowledge that I have to go through the same learning resources again by the time I need the knowledge. I have two learning modes. When I first come across a new topic, e.g. hadoop, I will go broad and skim as many learning materials as I can to get an idea of the lay of the land. Once I fe…
This. A friend of mine (senior sysadmin on a different team) has ranted about how his boss put tasks like "Learn Docker" in his list of goals for the year. First, such a task is hilariously underdefined. Second, if you're not going to apply the knowledge, it will be forgotten within a few weeks, and time spent studying it will be wasted.