What's the trick to improving usability? Users. A site can't be judged "good" or "bad" in a vacuum -- its value can only be determined by looking at how well it helps users get things done. That's why Forrester believes firms should adopt scenario design.

Scenario design helps users achieve their goals. How do you plan scenarios? Well, if you're designing scenarios for a commercial Web site, one that demonstrates return on investment (ROI) by getting sales, leads, or registrants, you design persuasive scenarios by turning the information you have on your users into personas.

Personas at their best evoke empathy in a process that's easily hijacked by technical imperatives and self-serving, company-focused needs. A design team must work with personas that seem like real people, people that can be conversed with, ideas bounced off of, joked with, related to.

Personas invoke this powerful human capability and bring it to the design process.
Well-designed personas are generative: Once fully engaged with them, you can almost effortlessly project them into new situations. In contrast, [designing for] a scenario covers just what it covers. Using a primary persona for your site design, or for on- and offline marketing efforts, is a lot like wading across that river. There's simply no such thing as an average person. Therefore, there's little benefit in summing your customers up into a bland, primary persona.

Unless your greatest desire is to design an average website with weak conversion, avoid average personas.

The differences your persona celebrates are critical to designing a persuasive Web site. Divergent personas help ensure relevancy across your entire customer base. This applies to more than just e-commerce and lead-generation Web sites. Effective personas work for a variety of applications, such as business-to-business (B2B), business-to-consumer (B2C), marketing campaigns, and products.