What was a simple business idea you had but thought it would be too vague to implement, only to find out years down the line a multi-million dollar business operating on it?
Just to preface: I think ideas are nearly worthless and execution is everything, so this isn't more than a "huh, neat." kind of reaction.<p>That said, back in about 2008, I was working a rather boring development job and pitched to my friend and colleague, who was a sports fan just like myself, that the best part of fantasy sports was the draft at the beginning and that the rest of the season was rather boring. That I'd rather do a daily draft of players playing that evening. We talked about building a prototype and I think I got as far as writing the statistics scraper. Anyway, it fizzled pretty quickly.<p>A few years a later, DFS is a huge thing. I didn't have this idea first, not by a long shot (<a href="https://en.wikipedia.org/wiki/Daily_fantasy_sports#Early_examples" rel="nofollow">https://en.wikipedia.org/wiki/Daily_fantasy_sports#Early_exa...</a>), but it certainly wasn't a mainstream thought back then.
Not a business yet, but I independently had the idea for maglevs/trains in evacuated vacuum tubes about 10 years before Musk brought it back to the popular consciousness.
For me, it was an app that lets you record the day's overall happiness level. I had even thought about details such as a way for asking user's name in a friendly manner if I were to build it. But now I know such apps exist.
in 2010 at a business pitch competition in Idaho at my college I pitched "pokemon crossed with geocaching" 6 years later pokemon go came out. I gave up on it because I had no resources or ways to approach making the thing.