I built https://explorehere.app to help you learn about the history of the world around you by sending a push notification whenever you pass a new historical marker on your travels!

It’s a freemium app with a pro subscription for advanced features; our revenue is just under $1k/month.

We’re working towards ExploreHere being a passive adventure guide. As you go about your travels ExploreHere will nudge you about interesting information wherever you go; history, unique things to see, special food known only in the city you’re in, etc.

I built an interactive Music Theory course 8 years ago over a winter break and it continues to bring in enough to pay my rent each month.

I just thought there had to be a more intuitive way to learn music theory than the very boring and jargon-heavy alternatives.

It uses Tone.js to include little interactive pianos, guitars, and other demos.

I've done no marketing, it hit the HN front page for a day, and after that initial spike in traffic has been fairly consistent over the past 8 years.

It uses Stripe for payments and for the first few years it was only Stripe. 3 years in I decided to add PayPal support... revenue doubled overnight, mostly from international customers.

https://www.lightnote.co/

PhD in math here with several published papers. And my recommendation is a metaprinciple: enjoy mathematics. Benjamin Finegold said similarly that the secret to chess is to enjoy every move. Personally, I had no trouble in mathematics, ever. And I think the reason for that is that I really enjoy just doing it, writing symbols down, learning about new theories, and even inventing my own.

Not everyone will enjoy mathematics at first sight. But I think at least 50% of that can be explained by the lack of obvious paths to enjoy mathematics. Obviously, most mathematics taught in high-school is not taught as it should be: a cool artistic logical pursuit that has all kinds of fun in it.

So my advice is to really find a mentor who already has found that path and let them show you how to enjoy math.

Believe me, I've tutored a lot of people, many of which initially disliked math and found it difficult. But after a few tutoring sessions, I could see a little sparkle in their eye that said, "hey, this might be cool".

So before you apply logic, studying, and other tedious "productivity" measures to your math learning, make sure you find a way to enjoy it first.

Anna Karenina. Nothing mind-blowing. I didn't see a light in the sky.

I read a lot, fiction and non-fiction. When I read Tolstoy, I remember thinking "What sort of dark magic is this?" He drew characters in a way I haven't seen since. I _knew_ these people.

I remember this book, decades later. I remember a lot of what I've read, but Tolstoy was the man. I have no idea how or why his magic worked.

"The best book I've ever read was Atlas Shrugged in 8th grade. Changed my life."

Not because I remember anything about it, or believe anything it espouses, or even like it all that much, but because it's a useful filter for obnoxious people in meatspace.

If someone I don't know too well asks me what my favorite book is, I say Atlas Shrugged. If they react inappropriately, I'll be cordial and treat them with respect, but I don't want to be friends. If they're way too supportive - the same rule applies.

If they're critical in a way I can appreciate, then I know they can either tolerate ideas they hate or have the social accumen to not go too hard in the paint early on in a relationahip. Really, I'm just looking for people who won't jump down my throat on a faux pas.

Later on in the relationship I'll tell them my actual favorite book, "A Canticle for Leibowitz", or "Neuromancer", or "The Dying Earth" (my opinion changes based on my mood).