Happiness, Misery, and the purpose of life: Nietzsche, Aristotle, and the psychology of flow
Happiness is defined by the greatest psychologists as living life in flow state, the state where challenge and ability are in the perfect ratio known. Argued to be the only remedy to the insatiability of man. The best way to grow is through the psychological theory of deliberate practice. One pushes themselves past flow state to the limits of their capabilities to achieve more progress at the cost of enjoyment. These psychological states match almost perfectly the philosophical positions of Nietzsche and Aristotle.
Aristotle's theory of happiness: eudaimonia, states that happiness is the end of all aims, which lies in rationality. Rationality in turn demands of one to live a life of virtue(living within the golden mean). The golden mean is the principle of the middle point between vice and virtue. Flow being the midpoint of ability and challenge, suffering and pleasure is perfectly fitting of this description.
Will to power follows the principle of overcoming. It is based on the condition of life. Natural selection being the process of life overcoming constraints and that being the underlying reason behind all drives. Flow fits into Nietzsche's philosophical worldview as the very purpose of happiness and pleasure are to be evolutionary traits beneficiary to overcoming the constraints of our environment. The difference lies in Aristotle identifying happiness to be a necessary natural conclusion of living out life's purpose(a life of virtue). While for Nietzsche overcoming(will to power) could lead one to a life of misery. As he describes in geneaology of morals(third essay:"What is the meaning of ascetic ideals?") when talking about the optimal lifestyle of the philosopher(The ascetic lifestyle which he describes as most of the time leading to a life of misery).
Nietzsche defines the good as "All that heightens the feeling of power in man"- The Antichrist (Aphorism 2). Where power is measured, whether in military conquest or in art Nietzsche leaves up to the individual. In what makes something great and powerful however there is a metric he applies regardless of the field. It is in overcoming, through the noble act of turning suffering and constraints into strength and power. One may be miserable but if in misery their optimum of power lies, then in it is their purpose.
Nietzsche's philosophy fits the theory of deliberate practice where one forces themselves outside of their golden mean of challenge and ability(flow state), and enters the optimum of growth where they are exposed to the hardest challenges that they can still handle. This is less enjoyable then flow state and may even lead one to misery, but if growth ranks to one above even their enjoyment then it is the right way of life for them.
One point both Nietzsche and Aristotle would agree on is that happiness is an internal state of mind based less in action(circumstances of the world), then reaction(how one interprets the world). Thus through practice one can alter what makes them happy to fit certain lifestyles. One could grow to love the suffering of deliberate practice, they could learn to love suffering and love fate. This is achieved through expanding the zone in which one is in flow state so that one day the greatest suffering is a challenge they can take and enjoy. If the happy slave is worse the the miserably king, the happy king is better then both and the most sublime existence.