I don't care what people say but being optimistic at all times is the worst thing you can be. If you are optimistic at all times then you are in a state of fully daydreaming. In your mind the underdog always wins; web site traffic pours like thunderstorm; money grows on trees; and stock market always goes up and so on...

At the same time being Pessimistic at all times is equally worse. In your mind you have the worst luck; you can never win; there are too many other people better than you; everything you try to do the opposite happens. People who are pessimistic at all times tend to not do anything at all because they say to themselves "if i'm going to fail then why bother trying!" and my answer is always "but if you don't try, you never know!".

Here is where the balance comes in, both optimists and pessimists are only right about half of the things and in the real business world they fully compliment one another. since examples are the best way to convey a message here are a few of them:
 

1)

OPTIMIST would say:
"We have a web 2.0 idea and when we make it and launch it, within 1 year we'll be like google"

PESSIMIST Would say
"We can never beat or match google so why bother"

BALANCE of the two results:
"It's hard to beat google, but we still have a chance to make good grounds, and what if we never get the traffic we need to make decent money so what do we have to do? lets plan this to the smallest detail"
 

2)

OPTIMIST would say:
"We have an idea and millions of people would want it"

PESSIMIST Would say
"it's a stupid idea because nobody would want it"

BALANCE of the two results:
"What would make a million people want it? and what do we need to consider if nobody wants it? Either way lets put our target getting a 1,000 customers first then we can worry about the next 10,000 and the next 100,000 and eventual million target"

What is the BALANCE?

Balance allows you to see things in perspective, like seeing both sides of the coin, it helps you plan for the best and the worst. Knowing about the worst things allows you to be prepared in case they happen, also knowing there even worse things that could happen also gives you enough motivation to be optimistic about even the little gains. Balance allows you appreciate you gains, your efforts and your life. It's helps you avoid pitfalls and makes every mistake a step closer the ultimate success.
 

So go ahead and be pessimistic and optimistic at the same time. It's only good for you!