Rules are a tool used to manage events at scale. If there weren't many things to attend to, then each situation could be examined individually and attended to based on the unique factors surrounding them.
One problem with rules is with precision. It's hard to set a square box with a precise area as a measure against which all square boxes are tested. Better precision means rules having unintended consequences.
If you decide that that people cannot put their finger 10cm in front of your face because it obstructs your vision, or more than 100cm in front of your face because that would cause some other kind of problem with some other thing, that leaves people with between 10cm and 100cm to put things in. The problem with that is that putting things between those distances probably causes some other problem you had not envisaged, but of course the rule has been made and you do not want to change it so soon after because you do not want to look like an idiot. So yeahhh, 'unintended consequences' are a big deal.
Another is that the more precise you try to be with rules, the more interesting you make beating them, without technically getting in trouble. Once you decide that people cannot put things less than 10cm to, and more than 100cm away from your face. It all becomes a game; you've just created new fun activity. People are absolutely going to constantly stick their hands between 10cm to and 100cm away at the weirdest angles, testing to see how to achieve the same thing you were trying to prevent — obstructing your face — without technically violating the rule(s).