Emotion is usually considered to be a feeling about or reaction to certain important events or thoughts. An emotion can be either pleasant or unpleasant. An individual also may have a mixture of both pleasant and unpleasant emotions. People enjoy feeling such pleasant emotions as love, happiness, and contentment. They often try to avoid feeling unpleasant emotions, such as loneliness, worry, and grief. However, people are sometimes not fully aware of their own emotions. Although most people believe they know what an emotion is, psychologists have not yet agreed on a definition that applies to both human beings and other animals.