I’m lucky Fully Automated’s primary mechanic is both flexible and simple because I’m here to tell ya, I’ve played D&D and I don’t think I could DM for that. Some folks are heavier on special game mechanics for each thing, and lots of rules, I treat my games more like collaborative storytelling with dice rolls just when the players want to do something cool or difficult. The big challenge for me is managing all the potential story paths on the fly and sort of adjusting what/when certain events outside the players’ control should happen to manage the pace of the plot and keep things feeling cinematic. At this point I know my NPCs pretty well and can kinda ad lib reactions to the players just fine, so sessions where I’m just reacting to the players are kinda easy - but when they set big events in motion I need to quickly balance what happens and try to case out where those events end. Does this push the bad guy to try and confront them directly? Should one of their informants call in now with the information they asked them to find last session? Stuff like that where I know it’ll adjust the course of their story. So I guess I’m mostly constrained by “what would happen” - what feels reasonable or believable for characters, some of whom the players don’t even know about yet!