"A virtue to be serviceable must, like gold, be alloyed with some commoner, but more durable alloy"

This quote by Samuel Butler is a metaphor for the importance of balance in life. He is recommending that, like gold, virtues should be combined with more typical and long lasting elements in order to be useful. In other words, virtues must be tempered with functionality and realism in order to be effective. Without this balance, virtues can become unwise and even harmful.

For example, an individual who is too generous may wind up in monetary difficulty, while somebody who is too truthful may be benefited from. Similarly, an individual who is too enthusiastic might end up being ruthless and overlook their relationships, while somebody who is too simple may be made the most of.

For that reason, Butler is suggesting that virtues should be stabilized with sound judgment and practicality in order to work. This balance is important for a person to be effective and to lead a satisfying life. Without it, virtues can end up being a hindrance rather than an aid.