In civ IV, I repeatedly would research worker techs and build cities in locations and then send workers to hook up certain resources which were under forests or jungle without having slavery or iron working, then spend 20 minutes talking myself out of opening the WB to edit out the forest or jungle.
Also in civ IV, would avoid high production sites far away from my capitol because the corruption would eat away most of its production anyway, only later to remember there is no corruption.
Also in civ IV, kept targetting a specific wonder and so would start a palace prebuild for it.
I had a hard time overcoming my civ III habits.
I also thought the promotion system was stupid and never paid any attention to my units' exp or promoted any of them, thinking there was no real advantage or strategy attached to it.
And I also once let a barb axe take my capitol defended only by a warrior, thinking if it lost I would only lose a pop or some gold or something, imagine my surprise.