"Sharing is a prosocial behavior, meaning that it is an action intended to help another person. It requires empathy, altruism, and most importantly, must be volunteered (in order to genuinely be considered as “sharing”). If these sound like complicated terms for a toddler, you’re right. Sharing takes a level of cognitive ability and understanding of the concept of fairness, which most young children are still in the process of developing. This means that sharing is a developmental process, and it takes time."
The above is an excerpt from an amazing article on mamainstincts.com, click here to read the full article.
At times, from our adult perspective, force a child to share. Because we understand the social etiquette and we so desperately want our child to be liked and well received. However this is counter productive to the child's understanding and development of sharing. Rather the child views this experience as being robbed, and becomes resentful and can create a negative view on sharing in the future. Becoming even more reluctant and defensive of their possessions.
Rather then force sharing, divert the others attention from the article, and encourage play with another resource. Leaving your child the room to grow in their development. Because although sharing is caring, it does take time to develop the caring aspect!