It matters less on what u choose and more on how you do it.
Don’t worry so much about skillsets. Search for understanding and patterns instead.
Try to resist the urge to put learned things under a label. It’s usually not the case that, for example, people are either skilled or unskilled at writing; it’s quite often not the case that one is an unskilled writer before taking a writing course, and a skilled writer after completing the course.
Examine notions and labels. For example, are formal methods a field of study? If one is skilled in formal methods, what does one know how to do? One might start by examining some particular formal technique, as embodied in some particular tool, but that examination grants competency with the particular tool and not with formal methods in general.
Indeed, people are often too eager to list themselves as members of some certain tribe based upon their skillsets.
If you don’t care about employability this is great advice.
I think I never really decide, I stumble on something I don’t know or know very little of and choose to dig deeper (or not). It usually ends up with something that will not improve my employability like learning Z80 assembly for example.
Nice article. I think we shouldn’t worry about the optimization of learning too much. You should find something fun to learn about that is adjacent, as you say, to your current path. But I think it being something fun to learn is the most important thing at least for me as it will keep me interested.
A helpful rule of thumb is that no matter what you pick, it’s going to be wrong at some level. Make peace with this and just focus on the higher level solutions rather than agonizing over tool choices.