Usually we think that happiness is found in the life which eliminates wholly unhappiness. When we are satisfied with almost all the parts of our life, but troubled by only one bad serious fact, we may bother ourselves about that one trouble and feel unhappy. So we think that every unhappiness must be avoided to be happy.
But on the contrary, sometimes it's said that unhappiness is required for happy. For example, the Bible tells us "Happy are you poor; the Kingdom of God is yours!" or "Happy are you who are hungry now; you will be filled!", in other words shortly but clearly, unhappy people are happy.
By Carl Hilty's happiness-theory, our unhappiness can be divided in two types. One is the bad result of malicious behavior and this is not useful for human. Another is the trial by God and this type's unhappiness makes each person so strong and pure that gives him higher happiness as a result.
Surely a human being usually through the fighting against his unhappy fact becomes stronger and deeper. We have the proverb, "In youth, man must bear troubles, even though seeks them". We can see in some unhappy cases recently too, that troubles or hardships make a human stronger and after all he can get higher happiness.