Let me guess...
You see a chick across the bar/wherever...she looks good to you. You then spend the next 10 minutes thinking about who she is, what she likes, what music she's into, etc. You then think about the 'look' your presenting at that moment, ie. the shoes you wore, what your dressed like (preppy/business scrubs) and start deciding whether you match up well enough with the look she's presenting and if she looks like the type who would find your current look attractive.
Then your spend another 5 minutes imaging what it would be like to date her, what kind of dates you'd have, if she'd turn into a bytch or if she'd love you for who you are, etc.
So you move a little closer, trying to get a better look.
Then you notice that her eyes seem like they could be a little too close together and you didn't like the earring she has on, which you didn't notice before. You also see her friend is wearing some cheap looking jeans and seems a bit trashy and beneath you.
Suddenly, your perception changes, and you decide that this girl probably wouldn't like the same things as you, and your friends wouldn't want to play wing men to her friends and in general shyt would end badly and you'd rather not go through all that work just to hurt her feelings in the end.
Did I about cover it?