It's generally not an instant addiction, the addiction to opiates usually happens over time. Your mind and body will become acclimated to opiates so subtly that you will be physically addicted before you even realize it. Do H, or any opiate, for long enough and you will become addicted, and you will suffer from withdrawls. Some people take longer than others to become physically dependent, but that doesn't mean it won't happen to you.

Now if you're going to smoke some H every once in a while are you going to be an addict? Of course not, but say you start off doing H once in a blue moon, and then it becomes once a month, and then once every two weeks, and then once a week, you're still not addicted right? Then you start to get cold sweats out of nowhere. You think nothing of it, but when you smoke some H it all goes away, and then the cycle starts. H binge, getting sick from withdrawls, taking more opiates to feel better, rinse and repeat.

The general population might over-exaggerate the dangers of Opiates and Heroin use, but that doesn't mean it can't kill you and it doesn't mean you won't get addicted. Be careful, be safe, and know the risks.