I remember watching a show a few years back that discussed obesity. They talked about a tri-athlete that looked like all he did was sit on the couch and eat Doritos. Yet he bikes and runs many kilometres a day. On the flipside, I know some rail thin people who never exercise.
What is the moral of the above?
Never judge a book by it's cover. I am sure you've heard it before and you'll hear it again... you simply cannot make judgements on people without any knowledge of them. You, like the letter writer, are needlessly judgemental.