pessimistic optimistic

Sometimes you get to know some people and you notice their reactions before important things happens in their life. And you notice that most of the time they are quite convinced that it will end up wrong. This is what you see, something that it is called a pessimistic attitude towards the future.
As well it may happen that some people in your life get easily overwhelmed by feelings, be it huge joy caused by dreaming or deep pain caused by some facts.
Could it be that being overwhelmed by happiness of big dreams of tomorrow made a person to defend itself? To defend of something that is overwhelming and feel like a threat to stable emotional inner self.

No matter what the cause is (huge happiness or a small pain), a life form defends itself once it is loses control over its own life when it perceives a threat. Defending is also a wide notion for a human being, it may express by hurting even the own self.

It might be that the responses to a threat perceived from overwhelming could be a desperate search to stop the joy, or at least to decrease its intensity. If it is caused by dreams or hopes of a fantastic result of what it is happening, the search might go into seeking any small thing that could make it wrong, in order to decrease the happiness.

Put it in other words: sometimes a feeling can overgrow, the optimistic attitude can overgrow and be felt as a threat, and in that moment one can decrease it through its counterpart, the pessimistic attitude. Or the other way around.
Are you deeply sure that a person is optimistic or pessimistic as you perceive him/her?