Electrical/bio engineer should explain this well: our brain is wired to like positive feedback, producing great amplification when a girl smiles to you, and we are high. Unfortunately more often than not the feedback from the girl (or FZZ for many) is negative, and we become low, and the brain seeks again and again ... often form other resources... sometimes by very 'low' means, and we become that girl hater, Fang hater, etc. etc.

Why life is so hard? It is because of all the rejections.