I've heard it said that "There is no key to happiness ... the door is always open." That reminds me that I'm the key. I make choices that lead toward more joy in my life. I make a choice on how to respond to a given situation: I can be angry and upset—or I can reframe it with a more positive spin and let go of whatever negatives the situation holds.
Choice. Sometimes you and I feel as though we have no choice. But generally we do. This definitely does not mean to ignore whatever pain, sadness or hurt we feel. It's important to be authentic and real even while we still choose to see the glass more half full than half empty.
Have you found the balance? It's really not a once-and-done thing either, is it? Each new day, each new situation may require making a choice about how we respond and how we see things.
If you do nothing else, perhaps even just posting the word "choice" on your bathroom mirror as a daily reminder can be a help in staying positive.
Since there's no "key to happiness," you get to open the door and walk through anytime you wish. Go ahead, push it open. See how life feels on the other side. You're the key.