I think it depends on the media you’re using: a postcard with blocks of text is less likely to be read than one with a few bullet points of text (esp. if the purpose of the postcard is to generate leads). I’ve learned that shorter copy works better than longer copy when the subject matter is simple, also. A complicated subject (product) obviously needs longer copy. I think “short” means different things to different people! I guess I should have clarified and said “don’t use 10 words when 5 will do.” That’s just good English and it can make the copy more clear.

Read your number 3: short and simple. Agree with the simple thought (but never dumb down your message, that’s quite different than keeping it simple).

But I and many statistics on effective marketing messages don’t agree on the short bit of your Kiss principle.
Your copy can never be too long, only too boring. It is a misconception held by many that long copy doesn’t sell, that many readers will not read long copy. Facts and profitable marketers will tell you different: the more you tell, the more you sell (even David Ogilvy knew that )

Karin H. (Keep It Simple Sweetheart, specially in business)