There are so may different factors at the core of negative mental health, but I would arguably say that poor health or a lack of focus on optimising the vehicle that gets you through life Is the number one cause. When you are lacking the vital components that have been evolved for us to operate as a human then your whole existence is out of balance. your mind can no longer be free to focus on growth or the attainment of goals because its so busy battling with the negative environment that you have placed it in. By sleeping well, optimising your nutrition and are exercising your mind is given the best tools possible to create a future that you want and to deal with the present outcomes of whatever life throws at it. The body and the mind are one, if you choose to ignore or destroy one the other will follow. once you health goes, that's it. Nothing else in the world will matter, you will be unable to do or think of anything other than wishing for good health. So do not ignore this. money, status and validation don't mean anything without good health.