Из последней заметке Реймонда Чена (элемент оф стайл):

You can’t just write «And that’s why X» to conclude your paragraph if you never actually explained why X. I read many paragraphs that took the form «Adults have quality Q. Quality Q means that XYZ. That’s why adults should have quality Q.» The paragraph did nothing to explain why quality Q is an important one for adults to have; it merely stated and defined it. One teacher explained to me that this isn’t a conscious writing choice but is rather simply a bad habit. «I’ve written a bunch on topic X. Now I need to wrap it up. And the way you wrap it up is to write, ’And that’s why X.’»

Интересно, а я так делаю когда-нибудь? Надо быть внимательнее.