How to stay positive?

So, one of my friends is really positive and she's always so perky. And I wondered how can someone be so positive and let nothing bring them down. One day I decided to start having a more positive attitude and I succeeded for two day then I was feeling negative again and I still do. How can I stay positive when negative things occur?
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So one of my friends is really positive and she's always so perky. And I wondered how can someone be so positive and let nothing bring them down. One day I decided to start having a positive attitude, I succeeded for two days then I felt negative again and I still do. How can I stay positive when negative things occur?
How to stay positive?
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