“Addiction,” Philip Seymour Hoffman once said, “is when you do the thing you really, really most don’t want to be doing.”

For Hoffman, the thing he really, really most didn’t want to be doing was take heroin. He had gotten clean, become one of the most respected actors in America. Then Hoffman decided it would be a good idea to go back to using heroin. The decision cost him his life.

Or was it a decision? Addiction is a complicated issue, where brain chemistry and free will collide. A lot of people think addiction is just a scam — the Get Out of Jail Free Card that jerks desperately wave after being caught, trying to be excused their misdeeds. Hoffman had been clean for more than 20 years. He was free. Or was he? Did he decide? Or did the addiction slumber within him, like a cancer, biding its time?

I can’t answer that one. If it was a bad choice, it was a bad choice that many make. Fifty percent more Americans died of drug overdoses in 2014 than died in car crashes: 47,000 people, a staggering toll. That in the face of such stats anyone would pick up a drug speaks to the human genius for both feeling special — bad things happen to other people — and for seeking that elusive zing across the frontal lobes that gives life savor.

Nor is addiction limited to drugs. There is booze, gambling, food, shopping. The one thing Anthony Weiner really, really most didn’t want to do was sexting — sending sexually explicit texts and pictures of himself online. It had already cost him his congressional career in 2011 and scuttled his bid to be mayor of New York in 2013.

OPINION

You’d think he’d learned his lesson. But whatever lure there is to that practice — and nothing is more baffling than someone else’s fixation — Weiner was back at it last month, with a “busty brunette,” who turned the resulting photos, one of which included Weiner’s 4-year-old son capering on the bed nearby, over to the New York Post. I wouldn’t have called sexting an addiction; but looking at the price Weiner and his family are paying, you have to wonder.

Weiner’s wife, top Hillary Clinton aide Huma Abedin, promptly announced their separation. The shame fire hosed at Weiner is soaking her and splashing her boss too. Ridicule comes naturally. Weiner’s transgression is a particularly noxious blend of infidelity, bad parenting, persistent fetish and lack of caution. Add to that the political motivation. Donald Trump is already playing in the puddles, wondering airily how national security might have been compromised by secrets percolating from Clinton through Abedin and dripping into Weiner’s sweaty hands.

I’m not a fan of the word “addiction” because it’s so overused. People say they’re addicted to chocolate when they just like it a lot. Who doesn’t? To me, addictions like alcoholism or gambling or, maybe, sexting are better described as compulsions, as obsessive mental disorders. As an alcoholic sober a decade, I still hear that voice, louder some days than others, saying “Now, wouldn’t this be a great moment for a drink!” The Beast in the Basement, scratching at the thick barred door to its cell. I have no idea whether Weiner ever seriously tried to give up his self-destructive ways. But obviously, he must have been going about his routine as a stay-at-home dad when a similar voice said, “Why do the dishes when you could be trading naughty photos with some stranger online?” Unfortunately, like Hoffman, he decided to listen.

Philip Seymour Hoffman’s line about addiction was taken from my new book, “Out of the Wreck I Rise: A Literary Companion to Recovery,” which the University of Chicago Press is publishing Monday. It was written with Sara Bader, who will join my pals Tony Fitzpatrick, Rick Kogan and Carol Marin as we read the chapter on the impact of addiction on family at 7 p.m. Sept. 8 at the Poetry Foundation, 61 W. Superior.