Naive
 Describes someone who is too trusting or innocent, often because they lack experience or knowledge about how things really work. A naive person believes things too easily or trusts people too readily.

Examples:
1- Maria was naive to believe that everyone she met at the party had good intentions. She didn’t realize that some people might take advantage of her kindness.
2- Some activists were naive in thinking that a single campaign would be enough to change environmental policies. They didn’t anticipate the long-term effort needed.