I'd say:
- Start with the first one, but in the context of the second one.
- Think about what you care about. "Stuff that makes me mad every day" might not be a bad way to at least kick-start your thinking. Your first answer to that will probably be something pretty general like "bigotry" or "ignorance" or "bad design", so you might have to ask some more questions to narrow it down: what, of that, affects the people you care about? What makes your life harder? What, of those things, can you turn into a problem that can be solved by what you're good at and what you like to do?
Personally I'm coming at this from having figured out, embarrassingly recently, that the #1 criterion for "should I do X" is "do I actually want to do X". I'm selfish and selectively motivated; I'm not particularly happy with that assessment, but I know at this point that I can't take on any project, no matter how worthy, if its success rests primarily on something I think is boring or don't enjoy doing. If you have more drive/self-discipline, maybe that is not a limiting criterion for you.
- Finally: there is something to be said for "never knowing", although I would look at that less in terms of simply wandering aimlessly, never knowing where you're going, and more in terms of: trust your inner instincts. It's not that you don't know where you're going; you just don't know yet. Accept that yes, you might be wandering, but if you're doing stuff you enjoy and think is interesting, you probably aren't lost.
I have this boss-figure in my head who always judges any experiments by their potential for deliverables. This person always wants to see results by Monday and has no interest in anything that isn't immediately, measurably pushing me forward in my career or my life. I'm learning not to listen to that person.
Because I have an increasingly firm belief that everything I do, no matter how weird or seemingly impractical, adds up to something. I was working on a blog of stories a while back, and I never launched it because I told myself people would think it was dumb, but that project is how I learned Markdown, and knowing Markdown comes in handy for me a lot.
I developed a fixation with programmatically re-using CSS animations instead of defining new ones—I'm explaining this badly, but it was a legitimate problem—and while the code I came up with was ultimately impractical and I never used it, I learned a lot about writing Sass mixins. That stuff, I use every day.
So I'm at the point where I'm willing to let myself go off and work on things I want to work on, even if it looks pointless and feels like messing around. I don't know where I'm going much of the time, but then there are moments when a bunch of things come together and it's clear to me that I really did, deep down, have a sense of where I wanted to go; I just needed time to get there.
Anything evaluated on the basis of "results by Monday" may get you from point to point, but I suspect all of us have some bigger picture waiting to be discovered—some important thing that only we are capable of doing. You really have to give yourself space, time, and patience for that to become clear. You really just need to mess around, follow your weird passions, and see what all of that adds up to when the dots are connected.
(Obviously, most of us have to have a job that pays the bills—I'm speaking in terms of how to think about where you're going beyond your basic responsibilities.)
Sorry this is so long. I hope I didn't come off as preachy or life-coachy here. I have a lot of thoughts on this topic because it's something I think about every day. (Despite how optimistic I might have sounded, I'm still haunted by the prospect that I'm an ADHD-riddled dilettante who's wasting his life, so your question is something I've been trying to solve for myself for a long damned while.)