One of the great things about programming is that we will forever be able to expand our skills. New platforms (like watchOS) arrive, new programming languages are released while the old ones evolve, programming patterns change, and some practices inevitably lose their relevance.
Software engineering, like engineering in general, is too broad a field to master completely. Gone are the days when a skilled programmer would know most of what all the other skilled programmers know, and to a certain extent, we must all choose what we will learn and what we will not. It is probably wise to keep up to date on a core set of topics and technologies that pertain to your interests and activities as a programmer, however, given our common position as WatchKit developers, I'd like to suggest a couple of pointers.