The part that says "I think, therefore I am". It's thinking that brought about this catastrophic identity crisis in the first place. Less '...why?' and more 'just 'cos' would make the human existence much happier. We would drink less coffee, there'd be no need for cigarettes to drive us to an expensive suicide. We wouldn't cling to our childhood and iron out experience for a brief glimmer of dying youth.
People not only should but WOULD smile more, Sandi Thom.
However, I like thinking. I get offended if people know something I didn't about a subject I thought I had thoroughly covered and I cannot wait to be old and wear purple. We should not only accept our fate, but embrace it.