Continuing the gamehelp for Mars: War Logs, Completionist is probably the second most problematic achievement people struggle with. Finish all of the secondary quests? Where you have divergent paths and one quest cancelling the other, come on.
Prepare to Doh! Edition. Don't know why I waited so long to get into this. Maybe it was the horror stories of how hard this game is? Well, I finally get to take some big bites out of it and a hundred "Dohs!" later realize I probably have some pointers to share for other potential grinders out there.