Great question! What seems consistent to you though was far from consistent. Some times we built the right product at the wrong time (ten years ago we worked on remote work audio software that made virtual rooms for people and I think there are 4 startups I know of working on this today), other times it was the wrong product at the right time, or we got everything right but failed to market it correctly (we built screensharing tools before logmein/gotomypc but pitched them as tools for customer support agents limiting our total addressable market). Additionally, you wrote “first decade” but most of the “hits” you know about today were created after 2010 (whereas we founded Fog Creek in 2000).
Stackoverflow was a great idea that Joel had and an amazing product that Jeff Atwood built - but the reason it worked so well in ADDITION to the product was that both of them had spent a decade building up a reputation with developers through blogging. If that hadn’t existed, I don’t know if that product would have succeeded so well.
We also struggled sometimes trying to figure out how much longer to work on something before calling it quits (I get domain name renewals still for projects that we eventually stopped working on).
I know none of that is really an aswer - but it’s just to say, none of it is easy. Often one thing we did is we showed people the behind the scenes of what we were doing and why (think the early days podcasts talking about Stackoverflow or Joel’s blog articles on Fog Creek and our bug tracking product FogBugz). For the audience we were reaching out to (mostly developers) this worked really well.
Trello on the other hand didn’t get much of its inertia from that - instead it was more our brand, and the flexible features of the product that drove its growth. We wanted to add features that let people express themselves through productivity software (which wasn’t normal at the time). Board backgrounds, cards that titled when you picked them up - we let people put more of their personality into their organization and it resonated. See more on this topic here.