Is not necessary that we need vitamins as much that this substances were so present in what we ate and almost impossible to avoid, that we adapted to use them for certain functions of our bodies. I think the same is valid for pain, it is simply part of any experience you ever had that it is necessary to maintain your mental health.
It was possible only recently to avoid this things, in the food this happens through the processing of the food that we end up with things like sugar that doesn't contain any vitamin. Through the modern inventions and innovations we end up increasing the amount of comfort that we live in, and eliminate so much of the pain that was previously inescapable.
Think of all the things you have in your house that serve no other purpose than make you comfortable. Simple inventions that we take for granted like chairs. How would you like to squat instead of sit on a chair?
In a primitive set-up avoiding pain is not necessary impossible as much as it is a lot harder. If you live in a straw hut wearing a leaf around your important parts, and you have to work every day for the food you are going to eat for that day, like going in the jungle almost naked to compete with predators like lion, and the only tool you have for the job is a refined stick with a pointy end, avoiding pain pretty much means death.
Even the drugs sucks, and requires some effort because there are no dealers. There are a lot of tribes that use certain plants that could be considered drugs like chew and smoke tobacco or the leafs of the coca plant the prime matter for cocaine. But this drugs are less potent then their processed and synthetic derivatives. Not to mention that you have to grow them or at least go in the forest where dangerous animals live to find any and if you did to many and can't work there is no welfare you will probably die from starvation. Addiction in all regards is a disease of modernity, it could simply not exist until a point in time.
The recent technology allows us to do so many things that previously were impossible, but also brought so much comfort that disrupts this natural balance. I am not against technology and comfort, contrary i love technology and comfort and there is certainly no way back to living in straw huts. I just think that we can improve and take in consideration this things whenever we decide how to live our lives. The same way happened with food so many people chose to follow specifics healthier diet to protect their health regardless that the food they consume every day it is less pleasurable.
Avoiding pain completely it is impossible, no matter what you do you will eventually experience some. I could argue that it is one of the few certainty in life pain and death are simply impossible to avoid. So if pain is impossible to avoid then what is the point, you are playing a rigged game in which no matter what you do and how you play it is impossible to win. Every moment out of your life contains some pain, regardless you like it or not, even when things go right there is something negative you can get fixated on.
