Your attitude can be altered by, quite literally, thinking yourself (insert emotional state here). It's a documented phenomena and used, with notable success, in treating mild depression and anxiety.
The opposite is also true. Hear something long enough, especially from a source that tends to be views as an "authority" on information, and you begin to believe it on a deeper level. In other words, repeat a lie long enough and it becomes the truth.
A quickie "Positive Is As Positive Does" From BabyBoomerExpress.com:
Think Yourself Happy
Can You Really Think Yourself Happy?
Believe it or not, it certainly is within your power to create positive thoughts allowing you to accomplish anything that you set out to do. Can you really think yourself happy? The answer is a qualified yes. Here are the ways in which positive thoughts can help you accomplish many things in life. It is widely recognised that 'thoughts become things'.
Positive thoughts produce positive results. We can either bemoan and whine about our situation, or we can change it. We can be negative about an event or we can be enthusiastic. It's entirely your choice!
President Lincoln once said, "Most folks are about as happy as they make up their minds to be." If you really want to think yourself happy, you can, just make up your mind to do so. It may be difficult to think happy in a world filled with hatred and violence. But it's not impossible. One thought at a time, one day at a time. One person, one idea, one positive thought can change society. How, then, can we make ourselves happy? By being a constant reminder to others that there is an abundance of goodness in the world.
* Seek out and find positive people to associate with.
* Expose yourself to all the amazing books, music and movies that are available.
* Find the one important thing in your life that inspires you, and pursue it.
* Practice random acts of kindness and respect towards others.
* Live life as if every day is your last. Smile.
* Use positive thoughts and words wherever and whenever you can.
* Use visualization to view the positive aspects of life.
* Speak in a positive tone of voice.
* Rid your mind of negative thinking. Perhaps you could try yoga and exercise.
* Let your expectations reflect your positive attitude.
* Allow peace of mind to be your constant companion.
* Become your own best friend. Practice TLC (Tender Loving Care)
Here is a wonderful poem which explains how unhappiness can thwart our every desire.
If you think you are beaten you are;
If you think you dare not, you don't;
If you want to win but think you can't;
It's almost a cinch you won't.
If you think you'll lose you're lost;
For out of the world we find
Success begins with a fellow's will;
It's all in a state of mind.
Life's battles don't always go
To the stronger and faster man.
Happiness is not a genetic trait we are born with. It can be ingrained in us by our parents and those we love. Or we can cultivate it from scratch, and nurture it within. It is up to us to maintain it, share it with others, and build our lives around it. Think happy, and you will be happy.