This quote by Aristotle suggests that moral qualities, or virtues, must be balanced in order to be preserved. Too much or too little of a virtue can lead to its destruction. This is often referred to as the Doctrine of the Mean, a central part of Aristotle’s philosophy.

For instance, courage is a virtue. However, if one has too much courage, it can lead to recklessness, which can be dangerous. On the other hand, too little courage can result in cowardice. Thus, the virtue of courage is destroyed by both excess and deficiency. The ideal, according to Aristotle, is to find a balance, a ‘mean’, between the extremes.

In terms of personal development, this quote can be a guide to self-improvement. It suggests that one should strive for balance in all aspects of character and behavior. Overconfidence can lead to arrogance, while too little confidence can result in self-doubt and inaction. Similarly, being overly generous can lead to self-neglect, while being too stingy can result in selfishness.

In today’s world, this philosophy can be applied to many areas, such as politics, leadership, and personal relationships. For example, a good leader needs to balance decisiveness with the ability to listen to others. Too much decisiveness can lead to autocracy, while too little can result in indecisiveness and ineffective leadership.

In personal relationships, Aristotle’s philosophy suggests that individuals need to find a balance between caring for others and caring for themselves. Too much focus on others can lead to neglecting one’s own needs, while too much focus on oneself can lead to selfishness and isolation.

In conclusion, Aristotle’s quote is a call for moderation and balance in all aspects of life. It highlights the importance of avoiding extremes and finding the ‘mean’ in order to preserve and nurture our moral qualities or virtues.