• Natural happiness - what we get when we get what we wanted.
• Synthetic happiness - what we make when we don't get what we wanted. It is as real & enduring as natural happiness because our psychological immune system works best when we are stuck.
• Psychological immune system - a set of largely subconscious tools that help us change our views of the world so that we can feel better about the world in which we find ourselves.

We synthesize happiness. "I am so much better off", "I believe it turned out for the best", or "I don't have any regrets", but we think of happiness as something to be found.

In 2 million years, human brain has nearly trippled in mass, gaining new structures... mainly the prefrontal cortex which most importantly acts as an experience simulator... have experiences in our head before we try them out in real life. No other animal can do this quite like we can.

Impact bias is the tendency for this simulator to work badly - things actually have far less impact, less intensity, & much less duration than we expect them to have.