As we’ve covered many times before, the purpose of a subject line or headline is, obviously, to persuade a reader that she must look inside. But if your tantalizing teaser promises far more than the email or newsletter can possibly deliver—or, worse, proves to be deceitful—you'll be doing your cause more harm than good.
According to Seth Godin, "The mindset of the brazen copywriter is, 'Well, even if only 1% of the people I trick are actually interested in the content, that's worthwhile. After all, there are a lot of people out there, and offending 99 to get one subscriber or one sale is good math.'"
Godin has another word for it—spam—and considers it a short-term strategy sure to wreak havoc on your company's long-term success.