For the most part when one is interested in a romantic relationship a person, they can be grouped into one or more categories of availability. This is of course going to generalize people, but it aids my metaphor so...

Subject falls under the category...? check all that apply

available
has significant other
not interested
interested
clueless to your existence
plays in another league
plays for the wrong team
plays a different game entirely

My point here is as follows:
I've met people that fall into these categories, and I've met people that span categories. Then along comes this girl. And she's cute, but as far as categories go, she doesn't even have a box to check. And even if there somehow became a box, it would have no meaning. And something frighteningly prophetic (well prophetic sounding anyway) is tapping at the back of my skull whispering.

That one. Be careful. That one there. That's the kind that changes your life.

This is not any thing as cliché as love at first site. This is something different. If I figure any more out, be assured that I will share.