In some cases its a personlity type
For these people, nothing is okay. It's too hot or it's too cold. It's too far; they're too tired; it's too hard. As the saying goes, these people would "bitch if they were hung with a new rope." Nobody pays attention to or cares about them enough; life is not fair. They didn't get the same deal or the same treatment as everybody else. Whine, whine, whine. These people experience the world as an agonizing and very personal ordeal. In response, the people around them want to slap them and scream, "Shut up and deal with it! But mainly, just shut up!"