Specially the following :
"They allow themselves to be happy:
As much as we all think we want it, many of us are convinced, deep down, that it's wrong to be happy (or too happy). Whether the belief comes from religion, culture, or the family you were raised in, it usually leaves you feeling guilty if you're having fun.

"Some people would say you shouldn't strive for personal happiness until you've taken care of everyone in the world who is starving or doesn't have adequate medical care," says Howard Cutler, MD, coauthor with the Dalai Lama of The Art of Happiness in a Troubled World. "The Dalai Lama believes you should pursue both simultaneously. For one thing, there is clear research showing that happy people tend to be more open to helping others. They also make better spouses and parents." And in one famous study, nuns whose autobiographies expressed positive emotions (such as gratitude and optimism) lived seven to 10-and-a-half years longer than other nuns. So, for any die-hard pessimist who still needs persuading, just think of how much more you can help the world if you allow a little happiness into your life.