OK, let me start by admitting that I am a dedicated optimist. I've even been known to opine that optimists are the only true realists, but that's a topic for another day. What I want to talk about now is project estimates.
When a project busts its initial cost and schedule estimates, an almost universal conclusion is that the cost and schedule were "too optimistic." Now, I won't deny that blind optimism, in the absence of facts and data, can cause problems down the road. And I agree with the observation that most projects fail at the beginning (tho we don't always know it until later). But let's not be too quick to put the blame on the optimists. Over runs might actually have something to do with project execution, unexpected developments, or several other factors.
When someone says "I can do this project for X dollars and Y days/months/years," they're guessing. This guess is made at a point in the project where we know the least. So please, let's not all be surprised when the guess turns out to be wrong.
But let's also acknowledge that a mismatch between the initial guess and the final outcome doesn't mean the guess was too optimistic. Maybe the problem had something to do with a lack of restraint on the part of the requirements writers. Maybe it had something to do with avoidable changes introduced long after the project launch. Maybe the estimate was perfectly rational given certain conditions, but changes to the conditions rendered certain assumptions moot.
And finally, maybe the problem was a naive belief that a 10-year estimate could have any validity over a 10-year time period. Even a pessimistic estimate is bound to be wrong over such a long timeframe. Bottom line: if you want your estimates to be accurate, make sure you keep the timeline short.