From Siegried Vogele's "Handbook of Direct Mail"
"Paper actually does have certain advantages over a representative. It waits longer, it can be put to one side and picked up again later, it can be shown to someone else, can be read quickly or slowly, several times or simple filed away for later. But above all, it does not complain when we throw it in the waste paper basket if it annoys us or if we do not like what it says, or if it does not tell us anything we want to know. This conscious throwing away could even be seen as a sort of substitute handling of the otherwise unpleasant task of getting rid of an unwelcome representative."
The thing is...he's (often) right. But only if you know how to write the letter!