Accepting emotions of all types, including frustration, sadness and disappointment, helps to create a more realistic worldview. By accepting these feelings as normal, it's easier to respond to them constructively. It also allows you to keep your expectations in check and to gain perspective about life.
Pay more attention to your feelings and how the outside world affects them. Do basic needs, like hunger, override your desire to be happy? Making a small improvement in your happiness may be as simple as being sure that you eat regularly and have snacks available.
It's also important to acknowledge the feelings of others. Maybe you're feeling good, but someone's sour mood is bringing you down. Recognizing these feelings as legitimate, or at the very least as a reality worth dealing with, can help to prevent you from becoming frustrated. Often someone who's upset just wants a companionable listener to turn to, and the result may be that you both are happier and more contented, having found understanding in one another.
Acknowledging feelings and emotions doesn't mean you should always act on them. Most of us are familiar with the advice to count to 10 or take a minute to cool down when angry. Similarly, trying to refashion negative emotions as positive ones can lead to real changes in mood. There's a kind of self-actualizing in play here: Tell yourself that you are patient and understanding, and eventually you will be. Embracing this kind of more optimistic viewpoint allows you to more easily let go of anger and to be more resilient in the face of adversity [source: Rubin].