I was going through my daily Google spam notification email, thinking about all the theoretical interests I have that now mostly show up as marketing emails. Democratic Party appeals, astronomy magazines, Optical Society information, TAXI songwriting promo offers, musical instrument sale offers, AOPA private pilot news, Japanese and French language study information, and much more. Most of these represent past or perhaps intermittently current interests, now mostly theoretical interests in that I do nothing with them 90% of the time.
Even the 146 apps on my iPad show this. So many astronomy, language study, music making, photography, and game apps that I hardly have time to even look at. But they don't take up any physical room, and you never know when some interest will strike again (hope springs eternal that 24 hours a day is only a temporary constraint). Books are like this too. An ever-growing backlog and I will probably never read 75% of them. I should at least clear out the many shelves of paper books that I am less likely than ever to read now that I'm totally hooked on the convenience of ebooks. But there I have the 10% problem -- I'm sure I will never need 90% of the paper books in my house. But I can't get rid of them until I identify the 10% I might need, and that is not a weekend project.
First world problems, I know, right? Such an abundance of riches. One that still grabs me is The Great Courses (this was the part of my daily spam that triggered this particular rant). College level lecture courses in every subject by some of the greatest professors in the world. I have a number of them as DVD and a couple as audio, and have watched or listened to a few lectures from some of them, but never completed one course. Yet I look every time for more, especially when there's a "big sale" (as there usually is). These days I rarely order any new courses because I know about my theoretical side. Like the way I'm a theoretical pilot and singer-songwriter ("flying singer," get it?).