This happened recently; I was trying out Fyrons Quad Mod with high tech and TDM races. I was hell-bent on colonising every planet in my home system before spreading out. I had managed to do it and built-up some kick-*** defenses. I started sending out some survey ships to start spreading out. The new turn started and I read that a star had been destroyed. Oh no! The AI had the same idea as I did (I had two star destroyers being built). It wasn't until moving further down in my Messages that it clicked in my head,
That was my home system's star!! I had forgotten to build a system shield!
Whether I was defeated by the AI or my own stupidity is your call!
