Addiction starts with the release of certain hormones as a stimulus to an action. Why do we eat fast food? Well the mixtures of fats, sugars, etc. produce a stimulus that makes us "feel" good. The hormones are released and we really like it! Why don't we touch electric fences? We tried that once and the stimulus didn't provide us the "feel good" response.
I think the threshold for addiction is a lot lower than most people think. If that pathway of hormones and stimulus continue to happen again and again, month over month, year over year then the brain begins to create deeper and deeper "tracks". Like the old dirt roads that wagons would travel down. Eventually, there would be a rut where the wheels of every carriage would roll down. Pathways in the brain can work the same way with repetitive actions. Thus habits are created and habits can turn into addiction based on the action/substance.
It's a fine line to walk which is why the Church's standpoint has always been abstinence.
When I was a young man and was prone to speak critically, my father would say: “Cynics do not contribute, skeptics do not create, doubters do not achieve.”
-Gordon B. Hinckley