In the case of drugs/alcohol, it actually does have something of a guhnetic component with how easily you're addicted, my family on both sides being an example. Everyone who's died for the last three generations has died as either a direct result of being an alcoholic (or in two cases drug addicts) or from complications resulting from decades of alcoholism. It can be overcome with willpower, but my mom raised me and my siblings knowing what the signs of alcoholism were from childhood and having a strong support network is really important for avoiding addiction. I'm not saying it's out of addicts' control by any means, but if you're genetically very susceptible to it and you don't know it (and you're also in a bad spot with no support) you can easily kill yourself getting hooked very quickly on things that normal people can do every weekend without issues. Again, discipline is absolutely the key, but some people are physically/physiologically much more easily addicted than others  That said, you won't die or land in the emergency room for donut withdrawal.