A Facebook honor-the-troops picture I don't get

You know, I enjoy most of the captioned pictures I see on Facebook. And I normally at least understand them. But I've seen this one a few times now, and I think I must be missing something.

Complaining about the heat on a summer day is showing insufficient reverence for soldiers on active duty? Does anyone know any actual combat veterans who think it's a sin to complain about heat waves? I've certainly never run into one.

Tags: us military