He's just not into you....

This is a line I just heard in one of my favorite shows, according to Carrie Bradshaw's boyfriend, if a guy doesn't call or show an effort the bottom line is that "He's just not into you." Now, I know it's just T.V. but really, that's a liberating thought. In fact I found out there's a whole entire book devoted to this theory. Girls tend to imagine and hope in a guy's intentions when really he may not have intentions at all. Then usually the girl ends up putting her hope in it, making excuses for the guy's lame non-existent effort and just ends up getting hurt in the end of all of it. If that was truth, then in protection of the heart, wouldn't it make things so simple for the girl to simply forget about him and come to terms with the fact that "he's just not into me" and move on, no more hoping, romanticisizng, or thinking it's something it really isn't. Shouldn't the girl have in her mind that "she is worth it" to make the effort for? Rather than making some excuse for some jerk?
Another thought/question, if one person is interested and the other isn't, isn't it just eaiser not to develop a relationship to start with? Wouldn't it be easier on the other person than coming to a place where you have spent time with them and eventually have to have "the talk" and hurt them even more by telling them there's nothing in store. What hurts more? I think the latter. So, why not just save the trouble and not even go there. But then again there are so many relationships that develop becuase someone gave the other person a chance even though they weren't intially interested, and ended up falling in love. Oh, i don't know, but I would love to know what you think.......
Another question, does the "spark" really exist, is there "one person" out there or could there be a lot of different people you could work with?