Another thing that's often confused for realism is detail. People see a set of rules that goes into great detail on something, and assume that just because they're detailed that means they're realistic. As an example, Traveller The New Era had a sourcebook called Fire, Fusion and Steel, which had really detailed rules on how to build all sorts of weapons and vehicles and maybe other things too, where you would calculate things like focusing distance on lasers and muzzle velocity on slugthrowers to create weapon stats... but in the end, they still plugged into a system where a PC could take a 9 mm bullet to the head once a week and only be mildly inconvenienced.