I would be interested to hear about any developments/ideas that you made in your work/life that were initially considered a minor aspect or feature but looking back you see that these were key decisions. Things that ended up being your key differentiator or selling point but were at the time of implementation "just another" thing to do.
On a more practical note, it turned out that the software project had one really, really useful facet: it sat on top of (and allowed) a nearly infinite variety of easily templatable content creation tasks, for which the Internet's existing answers were uninspiring to say the least. At the time I was not exactly a naive babe in the woods about SEO, and I knew that would be helpful, but I had no clue the extent of how helpful. I don't know if I would have failed but for that marketing hook, but it was huge for me in my early days and still represents a major chunk of my business.
I was hired out of college to work for a NYC-based startup called 'Games Media Properties' that ran a video game tournament called the World Series of Video Games (both horrible names, I didn't come up with them).
We spent roughly 300-400k per event to throw these huge productions, then another 1-2 million to film a TV series about it. There were 7 events, 3 in the US and 4 international.
The business model was a mix of ticket sales ($80 competitors and $5 spectators paying to come in), and ad sales (pay and be a sponsor).
Each event attracted around 30,000 attendees and we were asking for $1 million to be a 'title' sponsor of the series.
You can do the math on your own, but it essentially equated to $1 million to reach 30,000 people (assuming there was 1 title sponsor per event).
At the same time, we were building a few websites around the tournament. One for news coverage, one an actual 'tournament' site, etc. We had the idea to sell ads for our online sites with a near-inverse value proposition: Spend $30,000 to reach 1,000,000 people.
Needless to say, we stopped doing tournaments about two years in once all the advertisers flocked to the online model.
That company is now called Giant Realm and is an 18-34 male-focused ad sales organization that was recently acquired :)