2018 was the 25th anniversary since I founded Stardock. I was a college student then and I had no idea what I was doing. As an engineer, my skill set was in problem solving not in business or people or negotiation or accounting or marketing. Luckily, my problem solving skills allowed us to survive a lot of mistakes and learn from them. But to learn from a mistake you have to make it.
So here are the ten biggest mistakes I made in my career (so far) in ascending order to my biggest.
#10 Not networking with others
As with many engineers, I was not a people person. So I never found any value going out to GDC or other industry conferences to give talks. For many years, I was frequently invited to give a presentation on some new tech we had done by Microsoft or IBM or organizers of various shows and just declined because I just didn't see the value of using time to fly out somewhere to talk.
As I got older, I recognized that this was a big mistake because, being located in Michigan USA, I didn't develop the kinds of industry contacts or partnerships that I should. I've been friends with Soren Johnson, who designed Civilization IV (and is my partner at Mohawk) and I've seen the dividends he's recouped from investing time into attending conferences.
#9 Creating a Twitter account
This is pretty obvious now. Until 2012, very few people would have considered me even remotely "controversial". My politics are extremely bland. I'm maybe mildly conservative, libertarian? But I have very little passion either way because while politics interests me from a game mechanics point of view, the issues do not.
Nevertheless, I would say now I'm considered controversial in some quarters of the game industry because I've tweeted my opinion on various topics over the years. Opinions I still hold to be true but don't consider particularly controversial.
Examples:
During #Gamergate I repeatedly opined that yes, the gaming media often covers things based on their personal relationships and politics. This has nothing to do about "harassment" of anyone or whatever twisted version of #gamergate its opponents have imagined the controversy was about.
For those of you who aren't familiar with #Gamergate, here it is in a nutshell: Some game journalists got caught giving preferential coverage based on their relationships and politics. This was an open secret that I thought everyone knew about anyway. We'd gotten lots of coverage because I've been friends with people in the press. It's like every other industry.
The main difference is that the gaming press was much more obvious about their politics than say the tech press. I don't worry about our software products not getting covered because a journalist doesn't agree with whatever politics they think I have. The gaming press? Yea, it's a mess.
But now, of course, thanks to social media I'm frequently accused of being a racist, homophobe, transaphobe, and various other things that have no relationship with reality. We did a charity event with Humble Bundle and actually has so-called "activists" harassing the charity because they were working with us. That's how insane social media has gotten.
#8 That damn email
Probably the dumbest thing I've ever done is send an angry email to an employee who clearly had an ulterior motive. This employee and I hadn't gotten along in awhile and in hindsight, I should have let her go long before but she was actually very good at her job, I just felt she had a terrible attitude.
Anyway, after she had criticized a couple of male colleagues for highlighting their hair (in front of other female witnesses) I teased her about bleaching her hair which made her very angry.
The next week, she sent me an email demanding that I cease making "sexist, vulgar and embarrassing" jokes around the office. Anyone who knows me would describe my humor as...well, "dad" humor. It's not crude humor so her characterization irritated the hell out of me. So I responded with the dumbest response in history, "Well I'm a sexist, vulgar, embarrassing person and if you have a problem with that, find another job."
People do dumb things when they're sleep deprived and in my case, I had been up for over two days working on Elemental (this was written on an email) and I already tend to be guilty of not having a lot of patience with millennial SJW types under the best of circumstances. Nevertheless, holy cow was that dumb and once it was leaked to the press, all context was lost.
#7 Letting Strategy First be our publisher for Galactic Civilizations for Windows
This almost killed us. So when we came over from the OS/2 market, we had no idea how to the Windows game market worked so we teamed up with Strategy First. Despite having paid 100% of the cost of developing the game, we never got paid and Strategy First later filed for bankruptcy.
Sadly, this was a trend for Galactic Civilizations. The original OS/2 version was manhandled by a company called "Advanced Idea Machines". We never were paid our royalties on that game either and their primary contribution was to create the ugliest retail box in history...

Ugh. That box.
#6 Hiring friends
#5 Not focusing the Stardock Strategic Investment Fund on fewer projects
#4 Not patenting ZIP folders
#3 Not making Elemental 64-bit from the start.
#2 Not porting Galactic Civilizations to Windows NT in 1996.
#1 Staying in the OS/2 market long after it was obvious that the market was going to die.