It is a vivid quality. (Exclamatory)

Optimism is a great quality. (Compound) = Optimism is a quality and it is great. 

It leads one to be happy. (Passive) = One is led to be happy by it. 

Only the optimistic people are accepted by all. (Negative) = None but the optimistic people are accepted by all. 

We should be optimistic about life. (Complex) = It is we who should be optimistic about life. 

Most of the people are not optimistic. (Affirmative) = Most of the people are pessimistic. 

An optimistic person is the most fortunate of all. (Positive) = No other person is as fortunate as an optimistic person.