Children think that when they have a desire for something that having it is the only thing that will make them happy. This is because children do not have emotions that are developed enough to understand the difference between happiness and gratification.
It can be challenging for parents when children behave this way as this desire can make them very difficult to deal with, unless they are given said item. It is very important though that the children understand that they cannot have everything that they want.
In the cases when the child does have the item, parents may find that they display very selfish behaviour over it. This might manifest in them refusing to let go of the toy and share it with the other children that they might be playing with. There are certain steps that parents can take however that will encourage their child to share with others and get along better in groups of children.
It might not seem like it, but in reality, children do like sharing their things with others. This can be seen when there are many items available, children will often encourage other children to join in, or have one of whatever is on hand. As children grow older, for the most part, this desire to share grows stronger, and this is something that parents should foster in their children. Children allowing others to share in their most important things is an important part of growing up.
To encourage a positive environment for a child to share you should make sure that they are in a situation where they feel comfortable. As well as comfort it is also important that they feel loved and accepted. These emotions are conductive to sharing as the child will feel as if the person they are sharing with cares about them.
If a child is in a positive environment, you will also find that they are more willing to wait their turn for things. You will also find that the child will deal better with the disappointment of not being able to get what they want all the time.