Basically, the cause was my startup. It'd been my dream to found my own company since I was about 15 years old, then the stars aligned when I was about 25. I had a cofounder that was very into the idea, my previous skillset was a good match, I had money in the bank to fund myself, and my parents were supportive. So I went full-time & full-speed on it, thinking "This is it. I'm going to make my dreams come true."

The honeymoon lasted for about 2-3 months, and then I realized I was miserable - miserable enough to feel my sanity fraying, in fact. I was doing basically nothing but coding, and it felt incredibly lonely & isolating. I thought that was exactly what I wanted to be doing, but...apparently not.

Google came around through an incredibly random series of chance meetings. I decided my startup wasn't going anywhere in Jun 2008 (my cofounder had quit in April to go to business school), when a YC startup contacted me looking for a cofounder. They ended up offering me 25% of the company, and that was when I knew I wasn't ready to be a cofounder - here was everything I'd dreamed of, and I just couldn't do it. Applied to FriendFeed, but was rejected, then figured maybe I shouldn't discount big companies - after all, virtually all of FriendFeed's team cut their teeth at a big company (mostly Google). Talked with a friend at EBay that summer just to get a sense what life at a big company is like, it didn't seem too terrible. TipJoy contacted me about being their employee #1 right around the time of Sequoia's "The sky is falling" memo, which I actually entertained serious thoughts about (I liked the founders), but I was like "I need to see what else is out there". Ended up being referred to Google by a friend from the HP fandom, and started there in no small part because they were the only ones hiring.

The irony is - I went to Google thinking that my dreams of having a big impact on the world were completely on hold, but at least I'd have weekends again and would probably learn a whole lot. But the more I relaxed and stopped worrying about making a big impact, the bigger my impact actually became. There was a time, shortly after the visual redesign, where I started reverting to my previous lone wolf attitude and started a couple projects all at my own initiation, where I was the sole/primary developer. Both were canceled, and many of my other 20% projects never went anywhere. When I started asking around about what else was going on at the Googleplex, I ended up as an early engineer for Google's Authorship efforts (which at that point was nothing more than a dream), and consulting for the visual redesign of 2011, and doing a few of the homepage doodles. I never planned to be a part of the GFiber launch; I had other plans going on at the time, but they needed an engineer, and it seemed cool, so I just dropped my plans and volunteered to help out.

I'm still not all the way there yet - I still have occasional dreams of doing something great and want to just work all night to force my vision through. I suspect that if I could actually banish them, and accept what I am as completely enough even if I never accomplished another thing in my life, I'd be ready to found my next startup.

So, if you don't work for Google or Twitter but want to be a part of cool things, I'd start by keeping your eyes open for cool things. Ignore the tech press; they're usually the last to know about anything cool, and they usually go for the appearance of cool over actual coolness. Judge with your own eyes. Look for offhand mentions on forums, and then follow-up and research anything you see where you don't know what it is. (I found FictionAlley this way - a bunch of people were dissatisfied with fanfiction.net closing their forums in the summer of 2001, and said "We can do better", and a bunch of the writers I followed started mentioning them in review threads. I found Lisp and Haskell this way too, Lisp off Paul Graham's writings and Haskell because comp.lang.lisp dismissed it as just another "weird language"). If you have a pain point in your own life or your friends' lives, go search online to see if anyone is working on solving it, and if they are but it's not quite there yet, offer to help. Most people love offers to help on their projects.