And this doesn't just apply to tech startups...
The business I currently run (an exotic car rental company) started out precisely as described -- it was an idea I had to solve a problem I was facing (I wanted to rent a super-fancy car to drive across the country. Nobody in NYC offered that service). The business started as a fun side-project - a toy. I figured it would be a hobby business - something I could do in my spare time while I figured out what business I "really" wanted to start. I built it myself - did the deliveries, threw a website together, learned SEO, etc.
And sure enough, I was surprised by how much other folks also wanted this service. So when I went live - the calls kept coming. That was 8.5 years ago, and the business now employs over 20 people and is about to open in its 3rd city.
So take PG's words to heart - they're some of the best I've read.