I believe that being happy does not mean never being sad, but that happiness is something more global in terms of life. I mean, it's not a particular moment, it's our whole life, the process of how we live our lives. I believe that happiness for each person has its specific criteria, but in general, I think that happiness implies leading the life you want (not perfect but one that fulfills / has fulfilled the most important things for you) like: study / work in what you like, have a good support group (family, friends), make the hobbies you like, have a good partner, have the necessary capital to give you the life you want (simple or expensive), know you, and feel good with yourself. ... I mean implies, have time, money, affection, self-esteem and self-realization. For me it implies one more thing: to have opportunities, and to be able to choose.