That I wanted to be a software developer more than I wanted to be a writer.
I grew up believing I wanted to be a writer. All through the first decade and a half of my career in software, I felt like programming was just something I was doing to pay the bills while I wrote in my free time. In the mid-90s, I finally achieved my goal: I wrote a column for the San Francisco Chronicle. I wrote articles for Wired and New Scientist. I even got paid - a lot, really, though anything at all would be more than most - for writing fiction for a web site.
And I really didn't like it. This was a hard pill to swallow. The actual feeling of sitting down and finding something to say was painful. If there wasn't a looming deadline, I didn't do it. If there was a looming deadline, my life became a misery of half-finished sentences and sleepless nights. I completely went to pieces when I was in the late stages of finishing a piece. It was horrible.
It was certainly great to have written. Writing for the newspaper could be wonderful. It was a pretty remarkable feeling to be in a cafe and hear people discussing ideas that I'd just finished putting into words the night before. And writing for magazines meant that I got to sit down and play with robots with Will Wright, interview Pattie Maes about virtual dogs, hang out with the smartest guy I've ever met (Bob McHenry, general editor of the Encyclopedia Britannica) and talk to Richard Garfield about the genesis of Magic: The Gathering. I was invited to an ultra-special and extremely expensive "gathering of the digital elders," which was eleven different kinds of wrong. (I was invited in my capacity as a digital elder. Seriously. A lot of weird things happened in the first Web bubble.)
But it was just awful work, getting stuff out of my head and onto the page. Meanwhile, I still paid the bills by developing software, and it gradually dawned on me that I actually liked developing software. And that I didn't really like writing.
I spent the next 15 years approaching my work with what Thomas Lux once called "a positive condescension." The nagging feeling that I was missing something by working in software was gone. I ended up getting really good at it.