Positive thinking

Today we talk about positive thinking. Why people interpret most events as bad events? Most people undestand that every event has two sides - bad and good, but why we prefer bad? Does anybody nows?
For example, somebody has lost his job. Is it bad or good? Neither bad nor good. Depends on the way we look at that. Depends on our choice. We could be thinking: "Wow! Its great! I have lost my job! Good! That gives me an excellent chance to change my life! To see my mistakes and improve my personality. I have a chance to find something more excellent for myself. I have some time to have a rest."
But not. Most of us would be thinking:"Oh my god! I have lost my job! That's end! I'm dead! I wil never find an other job! Life is crap! My wife is going to divorce me...maybe. I so sad! What shall I do? I'm gonna kill myself. Oh god! For what?!"
Why humanes have such nature of thinking? What is the reason for this? How does the second (negative way) help us? I have no idea. What if we is pessimistic, would it give us more chances to resolve issues? NO. Conversely it will worsen the situation.
Definitely, the situation would be more better if we have positive thinking. It gives us power, makes our looking better, improve our creativity.
So, why we have an other nature?

'we talk' : we will talk / we are talking
'Why people interpret' : Why do people interpret
'undestand' : understand
'why we prefer' : why do we prefer
'nows' : know
'Depends on the way we look at that' : It depends on the way we look at it
'Depends on' : It depends on
'To see . . ' : A chance to see . .
'more excellent' : better
'But not' : But no
'That's end' : That's the end
'I wil never find an other' : I will never find another [one word]
'I so sad' : I am so sad
'gonna' : going to
'Why humanes have such nature of thinking?' :
Why do human beings think in this way/think like this ?
'What if we is pessimistic' : What if we were pessimistic
'it will worsen the situation' : it would worsen the situation
'would be more better if we have ' : would be better if we had
'makes our looking better' : makes our outlook better/ improves our outlook
'improve our creativity' : improves/enhances our creativity
'So, why we have an other nature?' : So why is our nature different/otherwise ?