Ever been in that situation? Were you over think everything and worry and wonder about what he/she thinks of you. You start to obsess over the fact that he talked to you for .5 seconds and wonder if it means anything. You start to see them and the hall and if they wave you smile a little, then quickly turn and walk the other way because each time they talk to you, you freak. You start trying to find reasons to be around them but each time you are you lock up. It's like you forgot how to use words. You then assume you have no chance because your afraid of rejection. So you give up. You crush yourself. 

Or maybe it goes like this. You meet someone and you two talk. Everyday. You eat lunch together and walk to class together. When your arms brush, your heart starts to dance. You leave school smiling and it feels like your on cloud nine. You can't wait to see him the next day. You start to get attached. You start to overthink. You wonder if he feels the same when you look in to each others eyes. You wonder if he feels the connection. You soon find out it was all an illusion. He found somone else.