How do people get addicted to opioids?

I honestly wonder, because I’ve been on them before and never found them to be addictive in any way. I’ve been on: oxycodone(oxycontin), hydrocodone(vicodin), codeine, morphine, hydromorphone (Dilaudid), oxycodone and acetaminophen (Percocet), plus a morphine pump with “break through” morphine” I.V. boost. and I.V. tylenol (which is much stronger than regular tylenol and not an opioid) and probably a few others that I’ve forgotten.