system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is it that characters in video games often have difficulty to directly touch each other?

For example: I notice in some video games, like Skyrim (bad example probably), that when two NPC's give each other a handshake, their hands don't seem to be directly touching each other but rather have some air floating in between them or they will just partly clip through each other's hands.

Is this technically very difficult or just sloppiness in the development?
gpt
Technically very difficult. 

Most animation systems rely on some kind of 'skeleton' of sorts as a basis for movement, and then use distances from that skeleton to determine if something hit that character. (That's an oversimplification of sorts, but this is ELI5 so bear with me). This allows others to interact with the "surface" of the 'model' (i.e. touch the outer part of the body somehow).

It's fine for an arrow because that's a simple two-dimensional (maybe curved a little) path. But it's not for a handshake where the amount of math required to make one hand fit properly inside another and then grasp and squeeze and fold fingers and skin is pretty daunting. Getting that perfect is going to take a super-big lot of testing tweaking and adjustments, and enough players will let it go that it's not worth delaying a game's release date.