God, you've opened a can o' worms with this thread!
Where do I start? Well for one there's the fact I seem to be the personification of Forever Alone. Whenever I'm interested in a girl, it's the old 'oh, it's not you, it's me', or 'I just like you as a friend', or 'I'm already in a relationship (even though it turned out he was a prick)', or even an 'it's you, it's just you'. Hell I even had a girl out-and-out cut off all contact with me when she got a boyfriend, even though I hadn't said a word to indicate I was interested in her. Oh yeah, and there's my best friend, who I love with all my heart and I'm damn-sure she's my soul-mate, but I know nothing will ever happen because she's asexual (i.e.: she doesn't engage in any form of relationship).
Then there's more general sticking-points, such as the fact I'm gonna be paying off college fees well after I've retired, due to a complete absence of job prospects beyond flipping burgers at McDonalds. Or the fact that a second Great-Depression is almost certainly right around the corner because those arseholes in the Eurozone are too fucking stupid to realise their currency was doomed to fail. Then there's the encroaching threat of the SOPA fascism. Then there's the constant fear of World War III (I'm kind of paranoid like that).
Add to those the fact I'm stuck at college with a sexist, racist, nihilistic, egotistical, narrow-minded, quick-to-anger little bastard who I only put up with for the sake of maintaining a professional and civil social life. Then there's the fact my sister literally hates my very existence and cannot wait for me to move out so she can turn my room into a little personal-lounge. And the fact I feel like the messenger between my separated parents with my father's side of the family actively trying to poison me away from my mother while simultaneously treating me like a 6 year old (I'm 21). And there's also the fact that my grandmother on my mother's side has a rare form of Alzheimer's, and it's absolutely crushing to see her completely unable to string a sentence together, and to think that she's overcome breast cancer and the death of her husband (when I was very young), only to be robbed of herself to this.
Is that reason enough?