Voluntary start to it would be the chemical reactions in your brain.
Drugs and certain habits such as Excercise and gambling, become addictive due to the chemical reactions. Dopamine, endorphine are highly adictive chemicals and are released to grant us pleasure. then you have oxytocin, Noradrenaline, cortisol which contributes to addiction.
Anything can become addictive if it gives us enough dosage of Dopamine and endorphines especially coupled with the latters.
It's a survival and social chemical being exploited.
Like curiosity, Evolution can't programme us to be curious about specifics, so it compromises and makes us curious about everything.
Social media likes, clothes shopping, advertisements, they exploit our oxytocin. When we buy new clothes or see a like, it activates our social chemicals, but it's the social good feeling you get without the interaction. It doesn't last because it is fake exploitation.
That's all drugs and adictive activities do, exploit those chems.
Addiction is real, it isn't a disease, it's an exploitation.
Unfortunately that can lead to drugd giving physical addiction, those side effects are very painful, plus the added cravings, the shut down of Dopamine and serotonin. Quiting can be like trying to live without breathing. You are suffocating painfully until it dies.