system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How can some severe long-term alcoholics/smokers/drug addicts maintain full and healthy organ function?

How is it possible for people to be alcoholics/smokers/drug addicts for decades, but develop no liver / heart / lung / jaundice problems and live to a ripe old age? Why do some bodies cave in, and others seemingly remain indestructible?

Edit: To clarify, I don't mean no visible problems, I mean having a full medical and scans, and coming back clean after being on 4 bottles of wine a day for years, or no problems with lung function after decades of 60-a-day smoking, for instance.
gpt
when you take toxins into your body, you increase the *chances* of developing a disease related to those toxins.  we say things like, "smoking causes lung cancer," and that's not exactly wrong, but it's not a 1-to-1 relation, either.  just as some people who never smoke or work in dangerous environments will develop lung cancer, some smokers never will.

part of this is just chance, and part of it is that everybody is different.  there may be other environmental or lifestyle factors, too, like exercise level, mental stress level, diet, etc. that help mitigate some of the damage.  

but the numbers don't lie: most addicts will suffer predictable physical damage related to their substance of choice.