When you're talking passionately about a product or service, it's interesting to consider the power dynamic of you and your audience. Where you respectively sit in terms of the "haves" and "have nots" can go a long way to how your audience perceives you.
Think about the following scenarios:
You're talking to someone about your business who isn't in your field and has no experience with it.
They either don't understand your product or don't try to understand it, and the exchange is dismissed. When they don't understand your market, you dismiss their confused reaction. "You wouldn't understand the problem because you're not our target audience." You forget that the laws of logic apply universally and so, even to someone who isn't familiar with your field, you should always attempt to speak with sound logic even to outsiders. Not everyone needs to find your service useful, but they should at least understand why someone else would.
You're talking with peers
This is the blogosphere. You're talking to others who totally get your space and see the world from the same perspective. Your passion is admired and even contagious. The feedback you get from peers encourages you to keep walking the walk and talking the talk... and you quickly forget that not everyone drinks the same Kool Aid that you do. Getting unbiased perspective here is incredibly difficult.
You're talking with someone who needs something from you
This is what happens when you're a VC.