"Correspondences are like small clothes before the invention of suspenders; it is impossible to keep them up."Of course, I wouldn't say correspondences are "impossible" to keep up, but it does take some work. In this project, I have found that it is easier to write a letter to a stranger, someone I've never written to before, such as the many letter writers on the the penpal sites, than it is to write to a friend or even an established penpal.
With my friends, I want to say something important, something meaningful, so I put off writing those letters until I have time to devote to the art of crafting a letter. With new penpals, or even just fellow snail mailers who may never become penpals, the letters are often simple letters of introduction, which are fairly easy to write.
However, I do believe, it is worth the effort to keep up the correspondences. Good friends are so important.