When you spend a lot of time talking about happiness, one can forget that sadness has value, too. One thing I have always told people is that it is OK to mourn a loss. It is not just “normal”, but it is necessary.
What is not necessary is to remain in a rut of sadness and self-pity. One needs to mourn, then push the sadness aside and get on with making the most of this wonderful world we live in. The object of our mourning needs to be transformed from a sadly-missed part of our present to a wonderfully-remembered part of our past.
There is an interesting article on happiness versus sadness in Newsweek right now. Interestingly, the article makes a case for happiness, but not too much of it over the long run. Here is a quick excerpt:
On a scale from 1 to 10, where 10 is extremely happy, 8s were more successful than 9s and 10s, getting more education and earning more. That probably reflects the fact that people who are somewhat discontent, but not so depressed as to be paralyzed, are more motivated to improve both their own lot (thus driving themselves to acquire more education and seek ever-more-challenging jobs) and the lot of their community (causing them to participate more in civic and political life). In contrast, people at the top of the jolliness charts feel no such urgency.