In the book 'The Little Prince' by Antoine de Saint-Exupéry, a young prince travels from his home planet to Earth and meets various characters who teach him valuable life lessons. One of the characters he meets is a fox, who explains the importance of relationships and the concept of taming. The fox tells the prince, 'You become responsible, forever, for what you have tamed.' This means that when someone forms a bond with another, they have a responsibility towards that individual.