I believe the greatest mistake many of us did - me included, was to become too attached to this flight sim.
Perhaps because we invested so much effort and time on it, we started to feel too attached and emotional.
Clearly that was a mistake - and we were taught a harsh lesson for it.
The good news is that, thanks to that lesson, we (or at least me) discovered that there is a whole world of flight sims out there, waiting to be discovered and in consequence, we put this flight sim (DCS etc. ) in its proper place.
It is just another flight sim.
I would not call it a mistake. My hours spent on DCS A10C were very well spent and I do not regret any of it. I have taught a few people, some of them complete n00bs that didn't even know what an "OSB 1" was. I vaguely remember telling another about what the "FPM" was and what it signified. Learning how to ripple-fire all my Mavs in one pass was fun and my buddies and I flew "In The Weeds" so often we got better and better as pilots and as a team. I loved DCS back then, and I showed it by buying DCS BS2 despite having little intention of flying the Shark.
The mistakes IMHO were how the company carried on afterwards.
It's just a flight sim? Yes, and no. Notice how geeks and nerds rage and froth at the mouth when a movie tramples over their beloved book/series/genre? Similar. Yes, it's just a hobby. No, it's not "just" a hobby. Choosing to spend our free time this way means we are investing ourselves in it and becoming attached only comes with the territory.