When you write copy for a website, a landing page, a brochure, a banner, an email, or any other marketing or sales material, this is a great piece of advice.

Except, you should actually ask that question at word level: what is this word supposed to do?

Words take up precious space on screens, and the ones you are going to pick need to have the potential to change the right people. This is probably the reason why your marketing material is not effective.