Optimism, in general, is childish, unreasonable and most importantly, irrational.

That may be true, but what outlook is not? If you are looking for a rational basis for any perspective, you won't find a single one that survives a deconstructive analysis. To me, it doesn't seem fair to put Optimism to a test that no other worldview can pass. We are not rational beings, and cannot be rational beings, because rationality is a construct of our own consciousness. We are a ruler measuring our own length.

Things can only go better than catastrophe. But if things go badly, its is the pessimist who is best prepared, and who comes out on top.

This may be true. However, catastrophe is uncommon and unreliable. How about the majority of time which is non-catastrophic? Does the pessimist have the advantage there? Is there a perspective that is more optimal than that of the Optimist and the Pessimist?

I would suggest spending some time on Stoicism. I had a wonderful high school philosophy teacher that explained it to me as such: "mk, we cannot always change our situation, but we can always change our perspective. That is what the Stoics believed."

IMO people conflate the term 'stoic' with the goals of Stoicism. Stoics do not endeavor to be unemotional, but understand that the chains that bind your emotions to circumstance are an illusion.

I often say: "The things that you do are what you want to be doing." I believe this. I also believe that coming to terms with this gives a very useful understanding of yourself.

To separate nature and behavior to me is an absurdity. Do we say that a dog that bites children is a good dog? Do we say that a bridge that falls down is a sturdy bridge?

Can you be an optimist to the extent that it is sensible, and a pessimist as well? Can your behavior and your nature adapt to circumstance? I would never consider eating a corpse on an average day. That would make me a monster. However, if we crash in the snow-covered Andes and you die, I am going to eat your frozen flesh, and will not be a monster.

I have had personal struggles with depression. At times the only tool I had was the knowledge that time would bring me out. However, through trial and error, I have discovered that action is also a tool. The actual activity seems almost irrelevant as long as there is even an intellectual modicum of desire to do it, but I do believe that nature and behavior are inseparable, and action is a modification of behavior; thus action is a modification of one's nature.