I know what you're thinking: "We already all saw this movie", "It's pretty obvious", "We don't need any more information on this subject". Well, too bad. I for one happen to think that simplifying disinterest into that movie's principles is a crock of crap, so I'm adding my own spin to it. Here we go!
6. Your belief systems clash
You're an agnostic Jew, he's Catholic--like, really Catholic. She's a hardcore republican, you donate a generous portion of your time to campaigning for environmental legislation and have even started a "Save the Seals" foundation. Whatever the situation, your attitudes of life just don't clash. If the person you're into is avoiding you because of this reason, it's a good thing.
5. They just don't find you that attractive
Don't worry--this doesn't mean your automatically "ugly", obviously. People have all sorts of things they are attracted to and all sorts of things that turn them off. I've been rejected by various people for being skinny, brunette-haired, blonde-haired, tall, American, Eastern European-American, smart, and "overtly creative" (I'm gonna go ahead and translate that one as "weird" for ya.) Maybe the girl you like only likes skinny emo fellas, and you're anything but. Don't take it personally--the right one for you will find you enormously attractive just as you are.
4. They've heard things about you that aren't true--or just might be
Unfortunately, this issue extends far beyond high school, especially among tightly-knit groups of friends. If you're known for being a "man-whore" or if you're the girl who everyone hears is "crazy", reputations like that can be hard to shake. However, a person who is really interested in you will take the damn time to get to know YOU--no excuses. If your negative denotation is matched to your grape-vine connotation, though, then you have a lot of work to do before you get into a relationship, anyway!
3. You have completely different interests
So the cute, nerdy girl you're crushing on has a penchant for 1940s-era classic films and hypermodern architecture. You're a science geek who doesn't know the first thing about right brain pleasures and would rather think about new theories on quantum physics than watch Citizen Kane. No matter the combination, having vastly different interests and little in common is, unfortunately, a recipe often akin to disaster. They say "opposites attract"--riiiiight. You will be bored stiff if you get with someone who you share nothing in common with.
2. You come from completely different cultures--and they don't know how to handle it
Inter-cultural relationships can be a beautiful, enriching thing, but unfortunately there are still plenty of people who don't mesh well with others simply because of cultural differences and an inability to assimilate with each other. An American friend of mine would get repeatedly angry with her Chinese boyfriend because of language differences and his devotion to academics over her, and sadly they never worked out. Although inter-cultural relationships will always present challenges, each person should be willing to bend a little to accommodate the other person. However, if a person avoids all people outside their own culture, they're not someone you want to be with, anyway.
1. They were into you--but you messed it up by moving too fast!
Haha, okay, not necessarily. In most cases, you both did. I list this as number 1 because it is all too common and all too true. Ever been with someone who seemed "so amazing", so you slept with them on the first date, spent a WHOLE day/night with them on the second, and bought them a nice gift on the third? *slaps hand* No, no, NO! Bad!
Moving too fast is a sure-fire way to mess everything up, even if it could have been a decent relationship. Yes, it is entirely possible to lose a great relationship over this! HOWEVER...
I end with this statement, to nobody's surprise: no matter what, the person with whom you're meant to be will be there. Always. They will give you as many chances as they can. They will be honest to the core. They will be even more intrigued by you with every passing minute. They will trust you. One day, they will love you.
In short, here is a lesson, my friends, from the late, great Dr. Seuss:
“Be Who You Are and Say What You Feel Because
Those Who Mind
and Those Who Matter Don't Mind.”