joseph tainter's analysis of the collapse of complex societies reminds me of the challenges around attaining sustainable mental health. he explains how at a fundamental level, the collapse of a complex society (where "collapse" means a simplification of social structures) is related to dimishing marginal returns. if a civilization spends more time, energy and resources on maintaining itself for diminishing marginal or total benefit, it will decide to collapse its structures to a simpler form. this will result in another, more powerful or efficient (experiencing increasing marginal return on investment) civilization absorbing the collapsed one's population and resources either by conquest, migration or subsidy.
in times of stress an individual, who is a complex system, can experience diminishing marginal returns on investment in their own life. this may lead to apathy, depression, nihilism, suicide, or other paths to reduce the complexity of their experience. like tainter's discussion of collapsing civilizations, a collapsing individual needs a new source of energy to make their life sustainable. this can come in the form of therapy, exercise, inspiration, spirituality, a new job, a pay raise, or some other path which either reduce the marginal cost (in money or stress) or increases the marginal benefit (joy, reprieve, clarity, freedom, happiness, choices) for the continued investment into their life.
james baldwin once talked about how he broke up with a woman he wanted to start a family with because he felt that he had no future. this is from a conversation he had in 1973 with Nikki Giovanni, where he gives a host of eloquent and beautiful examples of the same essence: you need some source of new energy (which for an individual might be hope) which keeps you investing in your future. if you don't see a future for yourself, your not going to invest in greater complexity (such as starting a family).