Even the happiest people are sad at times. Things go wrong, and disappointments and losses happen. If we have an open heart and feel love then we also feel pain. But that is not a bad thing. Feeling sad means that we are able to feel. If someone tells me to never be sad about something then I think that person either lies or ignores their own feelings which are only suppression of things they may be scared to look at. Never accepting being sad (here I am at this unhealthy way of positive thinking) will start growing inside like cancer and eating that person up.