1. You really don't want to engage directly with customers, employees, etc.—you just want them to hear what you have to say.

2. You're not ready to create new roles, update process, re-distribute resources and budgets, re-train people, and revise old policies.

3. Social media actually threatens how you make money—but you pay lip service out of fear.

4. Politics.

5. You see it as a career advancing opportunity as opposed to a significant business transformation.

Reverse any of the...

A Brand Evangelist is a person who promotes your brand without regard for compensation.  Their reward is the association with your brand.   Your brand becomes part of their identity.  The goal of any brand is to find and cultivate Brand Evangelists who can promote your brand everywhere without costing you a cent.  Social Media provides a great platform for you to grow some Brand Evangelists for yourself.