In my experience, studying a topic deeply is similar to going to the gym. It requires that you dedicate time to it very regularly, and being regular is far mor

In my experience, studying a topic deeply is similar to going to the gym. It requires that you dedicate time to it very regularly, and being regular is far more important than the duration of individual sessions. Also like going to the gym, it's extremely hard to maintain the required regularity if you aren't enjoying it. The only way I have found to consistently work out is to find a deeply technical sport (BJJ, not that it matters) that I actually care to do well. It's the same with technical subjects; the only ones I'm able to study deeply are the ones I find deeply interesting. With this in mind, my advice is as follows: approach "deep study" in a playful way, and study topics that interest you without regard for whether or not they are "useful". The utility is never far behind, anyway.