This quote suggests that the level of happiness or unhappiness a person experiences in life is not solely determined by their circumstances or fate, but also significantly influenced by their personal temperament or disposition. In other words, it is not just what happens to us, but how we react to what happens to us, that determines our level of happiness or unhappiness.

Temperament here refers to our innate or natural mental and emotional tendencies. Some people are naturally optimistic, resilient, and contented, and these qualities enable them to maintain a positive outlook and feel happy even in the face of adversity or unfavorable circumstances. On the other hand, some people are naturally pessimistic, sensitive, and discontented, and these qualities make them prone to feeling unhappy even when their circumstances are relatively favorable.

This idea is very relevant in today’s world where there is a growing recognition of the importance of mental and emotional well-being, and a growing emphasis on personal development. It suggests that in order to increase our happiness, we need to work on improving our temperament or mindset, rather than just striving to improve our external circumstances.

For example, instead of just seeking to achieve more success, wealth, or status in the hope that these will make us happy, we should also strive to cultivate qualities such as gratitude, contentment, resilience, and a positive outlook, as these will enable us to feel happy regardless of our circumstances. It also suggests that we should strive to manage or transform negative mental and emotional tendencies that can make us unhappy, such as chronic dissatisfaction, negativity, or a tendency to dwell on problems or setbacks.

In the field of personal development, this idea can be applied through practices such as mindfulness, which can help us to become more aware of our mental and emotional patterns and to cultivate a more positive and contented mindset. It can also be applied through cognitive-behavioral techniques, which can help us to challenge and change negative thought patterns that contribute to unhappiness.