In this quote, Nietzsche suggests that psychology, or the study of the mind and human behavior, originates from idleness, or inactivity. He implies that only when one has enough free time and leisure can they contemplate the intricacies of human nature and behavior, leading to the development of psychology. The second part of the quote, where he asks if psychology could be a vice, suggests that he questions whether this deep introspection and analysis of human behavior is always beneficial, or if it could potentially be harmful or indulgent.

Nietzsche’s statement could be seen as a critique of excessive introspection or over-analysis, which can lead to paralysis by analysis, where one becomes so caught up in the details that they fail to take action. It can also lead to self-absorption and a distorted view of reality, where one’s own thoughts and feelings are overemphasized at the expense of objective facts or other people’s perspectives.

In today’s world, this quote could be applied to the phenomenon of overthinking, where people spend too much time analyzing their thoughts and feelings, often leading to anxiety and indecision. It could also be applied to the trend of self-help and personal development, where an excessive focus on self-improvement and introspection could become a form of narcissism or self-indulgence, distracting people from the practical realities of life and their responsibilities towards others.

In terms of personal development, Nietzsche’s quote might serve as a reminder to maintain a balance between introspection and action, between understanding oneself and engaging with the world. It might also remind us to be wary of becoming too self-absorbed or over-analytical, and to value practical experience and engagement with others as important sources of learning and growth.