Those down chemicals—call them the Here & Now s—allow you to experience what’s in front of you. They enable you to savor and enjoy, or perhaps to fight or run away, right now. The up chemical is different. It makes you desire what you don’t yet have, and drives you to seek new
things. It rewards you when you obey it, and makes you suffer when you
don’t. It is the source of creativity and, further along the spectrum, madness;
it is the key to addiction and the path to recovery; it is the bit of biology that
makes an ambitious executive sacrifice everything in pursuit of success,