I come from Britain, a country swimming in deprecation, self-doubt and cheerful pessimism, so it's been tough for me to learn the confidence I need to get things done. Often the confidence has to come from a gut instinct before there's any real evidence; as Tom Evslin says, nothing great has ever been accomplished without irrational exuberance!
What makes it hard is that you need confidence to take on seemingly impossible tasks, but most of the time your initial confidence is misplaced, they're actually impossible. That doesn't mean you give up, it just means as you learn more about the facts you have to change your approach or even your goals. I've spent a lot of time figuring out tools I can use to help me decide.
Most of them boil down to actively hunting down evidence. What I love about Customer Development is that you collect meaningful user feedback early and often. Even with only a few users, the Net Promoter Score and other surveys I've run have astonished me, and forced radical rethinks. I'm also a disciple of Bob Sutton's work, he's spent his entire career on a crusade for evidence-based decisions, and I love his phrase "Strong opinions, weakly held". If you don't have any confidence or certainty, you'll never persuade anyone to act or really test your own ideas, but if you drink too much of your own kool-aid, the psychological effect of confirmation bias makes you ignore important evidence against your theory.
So, where am I going with this? This is in the front of my mind because I'm sitting banging my head against the table because of the recent developments in the global warming debate. It's obvious from reading the leaked emails that the IPCC and Anglia University have their share of hubris, but I'm driven crazy by how evidence doesn't even seem to feature in the skeptics' arguments. There's an objective reality; either man-made global warming is occurring or it isn't. This isn't a philosophical or political debate (though the question of the right response is). Either it's happening, or it's not, and we have a whole process for determining physical questions like this, called science. It's flawed and uncertain, and the ClimateGate scientists were perverting the process by trying to keep critics away from their data, but it's built on a base of evidence. If you want to dispute the conclusions, you need to dispute that evidence, otherwise it's all just about who shouts the loudest.
Since I'm old enough to remember the coming Ice Age I've got a natural inclination towards skepticism, so I've spent some time going back to the basic papers underlying the consensus. Nobody I'm aware of is disputing the observed rise in CO2 levels, now the highest in 2 million years, and up about 30% in a century. I then dug out a paper that tries to quantify how much heat CO2 and other components in the atmosphere trap. It shows that CO2 is responsible for retaining a significant amount of heat, and again I haven't been able to find any evidence that this is in dispute. Volcanic eruptions are a natural experiment demonstrating that changing the atmosphere's composition can change the climate.
Take these conclusions as facts, and you've got significantly rising levels of a gas known to contribute to warming. Even if you throw out everything else related to temperature measurements and climate models, it's hard to escape concluding that there's a significant possibility that we're affecting the climate. There's legitimate arguments around exactly what will happen and what we should do, but if you're going to assert that global warming is a myth, you have to tackle the evidence directly. I would love to read reasoned arguments based on solid evidence about why I'm wrong, but the few I find tend to evaporate into mirages upon closer inspection.
Confidence is vital for getting things done, but it has to be a spur to test your theories, not a lazy substitute for gathering evidence. I'm very aware of this trap because it's one I keep falling into! I look back at the last two years of building Mailana, and I've lost months chasing lost causes because I didn't see what was right in front of my nose. The skeptics' attacks on AGW remind me so much of those wild goose chases, driven by a firm belief with no foundation. Please, throw evidence at me, but I'm tired of confident assertions with nothing to back them up.
What's wrong with confidence? It turns into a vice when it stops you wrestling with reality.