Pretty much. Or rather, if you can't just take it or leave it, you're an addict. I was addicted to nicotine for decades. I had very little willpower about not having another cigarette. It took years to really stop, to stop relapsing.

It may be that the mechanisms of addiction for meth/amphetamines, gambling, smoking etc is different from opioids, as I could to loads of the first, without ever having trouble stopping (just slept for a few days), while some of my friends had addictive behavior. It puzzled me, so maybe it truly is more difficult when relapsing on those.

After going through opiate withdrawals, I found quitting smoking rather pleasant in comparison. It's really not a ride you wish to take again.

Right, the main symptoms of nicotine withdrawal are nervousness and anxiety. I've also been addicted to diazepam, and that was similar, but more intense. I gather that symptoms of opiate withdrawal can be extremely unpleasant. I've had a few small tastes of that, after overusing oxycodone (and diazepam) for back pain. I'd never want to experience the real thing.

I've also done lots of amphetamines and cocaine, and never felt like I was getting addicted. Maybe there's a genetic component.

For me, alcohol was harder physically and harder to stop.