Let me give you a clue.
“The number of ideas to use in an ad should be odd – and three’s too many”
Timo Everi, Hasan & Partners Helsinki
I couldn’t put it better myself.
The key to any form of marketing is clarity (of course it also has to be persuasive, but for the purpose of this post, clarity wins through).
If you want your reader to be 100% clear about what you’re telling them you can’t bombard them with umpteen messages at once.
A classic example of this is a sales letter.
Years ago, a client wanted a sales letter. We agreed terms and I got to work. After a while he had a brain wave; by getting me to include 2 products within one letter, he would only have to pay me once to sell twice as much.
Trying to squeeze two ideas into one letter merely dilutes its effectiveness. To have any sort of effect you must concentrate on one idea and exploit it to the max.