A person who sees the good in life and a person who sees the bad in life both see the truth of things. The reality they live in, however, is very different.
Happiness is a choice. There is plenty in the world to make create happiness, and there is plenty in the world to create unhappiness. The world you live in is your decision. The world itself cares little which reality you choose; it will provide whatever you need to be happy or unhappy. The world you live in is up to you.