I like the nature/custom thing. In fact, I like it very very much
I will add that to my arsenal. Not so much different from my "it's arbitrary" response
("Why is it called a 'shoe'?" "It's arbitrary, people before us called it something that sounded a bit like 'shoe,' so we call it something that sounds a bit like 'shoe'")
And I've already been using "tradition," too, which isn't quite the same as "custom." Ok, I'm probably not supposed to be thinking about writing an "Opposites" book including "arbitrary/determinate" "nature/custome" "tradition/inovation," and "Predictable/unpredictable," am I?
("Predictable" is my response for things like "why should we wait for the little walking figure?" "Because to make traffic safe, it's best to be predictable, so it's worth following an arbitrary set of rules.")
-Mich