Most people don't know this but emotions only last 8 seconds on average. That means you have a chance to change your mood and your day every few breaths you take. So when you are depressed, angry, or happy all day, it is because for most of that day you have fed that particular emotion again and again with thoughts and experiences that evoke the emotion. This is how you establish a mood.
An unknown author wrote:
"Be careful of your thoughts, for your thoughts become your words.
Be careful of your words, for your words become your actions.
Be careful of your actions, for your actions become your habits.
Be careful of your habits, for your habits become your character.
Be careful of your character, for your character becomes your destiny."
This verse illustrates how each and every moment of the day and every action we take is valuable. They set up patterns for our experiences and the more ingrained the pattern, the more difficult it becomes to change.
Similar to the above verse, you should be careful what you think, for your thoughts become ideas. Be careful of your ideas, for they become beliefs. Be careful of your beliefs, for they become expectations. Be careful of your expectations, for your expectations shape your reality.
Our destinies are in our hands. If we allow more than a brief moment to be gripped by misery, it is like committing ourselves to a miserable destiny (if only for a moment). It is human and advantageous to be able to experience a wide range of emotion, but remember that emotions only last about as long as 4 heartbeats on their own. If you have negative emotions, it is up to you to limit their duration. If you have positive emotions, it is your responsibility to sustain them.
Nobody can make you feel a certain way. It is your choice to feel how you feel. Similarly, nobody can change the way you feel. It is up to you to change it. The choice is yours.