Liz: I think it's a huge mix of genetic predisposition in some cases -- one of the central themes of the book is the idea of nature versus nurture and how it can be that two siblings in the same family come out so different as adults. I think the answer to that is that there's -- certainly, some people have a genetic predisposition to it. Also, even within the same family, two people can have very different experiences of nurture, whether we're talking about birth order or whether we're talking about the circumstances of one's family when one was growing up. I think you see this a lot in families where there's a large age gap between siblings especially. The parents themselves can have, for example, completely different economic circumstances between when one child was born and the other child was born. I think all of those things contribute to why one person might suffer from addiction and one might not. I do believe that there have been huge systemic failures that have contributed to this particular wave of opioid addiction in the United States. I'm glad to see some legislation is starting to be imposed that protects the individual from the profiteering of pharmaceutical companies, but in a lot ways, the damage has already been done. This very insidious addiction has already made its way into family units. We will feel the effects of that for generations, I think.