Why don't we care about our pants?

It's raining today.  Raining hard.  We're s'posed to get ... I don't know ... several feet of rain in just a few hours.  OK, a few inches anyway.  So I came to work this morning and had grabbed only my keys, wallet, phone, and umbrella.  Parked the car.  Made sure to stow away my keys and wallet in my pockets, leaving both hands free (unusual, since I usually carry lunch, a book or two, and who-knows-what-else), grabbed my umbrella, got out of the car and locked it.  Began walking toward my building, rain coming down fast and from everywhere (mostly above).  And then a thought came to me that I have thunk (a wordicle!) quite a bit about:

I'm doing my damndest to cover my topside--head, shirt, arms--but evidently, aside from doing my best to dodge puddles, I don't care how wet my pants get from the rain.

Why is that?