I like this point in particular -- "Don't stress out too much about how valuable the things you're going deep on are." The general stance of people is to stick to the practical stuff -- knowledge or skills that you can use right away. But, it's important to have a long view and given enough time the impractical could turn into something practical. Serendipity is underrated, and in my experience the impractical stuff is what enables serendipity.