My 2c: Everything is relevant to some extent, and we're all students, just at different experience levels.
Like you were told, you don't know what you don't know, and there's a whole lot to know. I've been flying for 42 1/2 years, and I'm still learning. When I stop learning, I'll stop flying. Literally every time I go up with an instructor, I learn something, either something new or a way to do something in a different way from the way I'd been doing it.
There are guys on this site who've been flying for a whole lot fewer years than I have but who are much better pilots in some ways. I wouldn't trust me in a 180 with fat tires; but some of those who are great with TWs can't fly in the clouds or the ATC system, and I can.
As good as I am at navigating by reading charts and matching them to the terrain (pilotage), I discovered that some elements of chart reading was actually a weak point when I took my seaplane checkride last summer. What? Seaplanes and chart reading go together? Yup--it's not all stick and rudder.
GPSs are nice, but I can still shoot a pretty accurate NDB approach (if I can find one to use!), and there are enough NDBs still working throughout the Midwest that it's possible to navigate with them from Colorado to Indiana, maybe farther, by combining them with ded reckoning--which I'm pretty good at doing, too. I can find where I am with a single VOR by triangulating. But many people make the mistake of thinking that because they've got a nice GPS, that's all they need--yet it can be interfered with, and in fact all this past Fall, a good chunk of the southwest US had inaccurate and compromised GPS signals due to USAF testing, so that other navigational skills were necessary.
I can read the weather very well--but some of the nuances I thought I knew pretty well, I'm finding that newer methods have made some of what I "knew" less accurate--there's much more to learn, because there's been an amazing amount of weather research done in the last 40 years.
I guess I could go on and on, but you get the point--there's a lot to learn, and you can't begin to know what is relevant vs. what is irrelevant--and in reality that's because it's all relevant to some degree. Be an intellectual sponge; it'll serve you well.
Cary