"Addiction is when you fall in love with a drug instead of a child or a lover and the learning that takes part in that part of the brain is designed by evolution to get us to persist despite negative consequences to do what we need to do - because I don't know anybody who could survive a relationship or parenting if not for the ability to persist despite negative consequences. The problem is when that gets misdirected to a drug and then you can find yourself in some very negative and potentially deadly situations."