Why optimism is a vice

It is better to always assume that bad things are going to happen to you, not feel satisfy even when good things happen to you. Or always assume that nothing bad can ever happen to you, take big and unnecessary risks, accept a work load that it is going to lead to an unbalanced hectic life?

They both seem pretty unreasonable ways to live your life, regardless that you are a pessimist or an optimist. Virtue is the point between deficiency and excess, pessimism is about deficiency seeing the world as being a dark and cruel place where you have to survive the food chain. The other extreme optimism is seeing the world with the exclusion of the negative aspects of life. Everybody is nice and friendly, you can do anything you want, there is no failure.

The problem with this is that they are not accurate portraits of reality, the world is neither just dark and violent or happy and free of failure. You could say that when the reality from the outside doesn't mach the reality from inside your head you are in trouble.

There are good and bad things that can happen to you at any point. The person that is in either of this extreme denies certain negative aspects of life.

Regardless that you are talking about pessimism or optimism, both of them are strategies through which the individual denies that he can fail.

The optimist develops a blind spot because, he is not able to accept that failure is a normal part of life so he constantly engages in activities that proves him that failure doesn't exist and when failure happens he brush it away or wrongly justify it.

The pessimist deals with the chances of failing by constantly thinking of failure and anticipating it, the same way that someone that is having a hard time accepting death might develop an interest for extreme sports. By facing death multiple times and survive it he hopes that he will eventually become so numb and immune to his fear of death.

The pessimist hopes that by constantly anticipating failure he won't suffer when failure happens.    

If both of this are unbalanced ways of living your life, and could be considered vices, than what is the ideal way to live your life?

Optimism and pessimism are poor perceptions of reality they exclude either the negative aspects of life or the positive ones. Keeping a close grip of reality has to be important for your happiness, so in my opinion realism is the virtue between pessimism and optimism. It is the point of balance, because the realist doesn't excludes any of the possible outcome of any situations.

There are only three possible outcomes you can have in any situation. You either fail to do what you propose to do in the first place like you don't even try, the second possible outcome is when you try but you fail and the third is try and succeed.