Many people have some troubles in their business and daily life. Among them, I guess lack of confidence is the most frequent problem they feel.
A person who doesn't confident tend to feel that all other people than him are confident about the task they face. Then, people without confidence would avoid the challenge. It results in a failure, because he has not tried. It is obvious.
Lack of confidence is also widespread in people with mental disorders Who have anxiety disorders or avoidant personality traits are typical. They regret the potential failure before the result is determined. They hardly try anything without adequate assurance.
I never recommend them to tackle with confidence. I do not advise them to prepare for the task in advance, either. They make the situation worse.
Confidence itself has no evidence. Nobody predicts the future exactly. Whether the attempt will succeed or not cannot be proven before the real trial. If you succeed, the experience of success will become the confidence.
So, I recommend you to try without confidence. The idea that the success should be predictable robs you of the confidence. Try without confidence. If fail, stop it. That's all.
On the other hand, pretending to be confident is preferable. Most human trust a presenter of confident. The human includes yourself.
Some people think that they would feel more shameful if failed. It is a point. It is quite natural to want to avoid shame. However, we often disguise our own mind, especially after the failure. We tend to think as if we predicted the failure.
Therefore, at least in a business situation, to be confident and to express the prediction clearly are important, even if it makes you to take a risk of shame. After failed, you would learn more about it with a temporal shame.