Sometimes it helps to be an optimist not a realist
The subconscious mind can process 20 million bits of information per second. The conscious mind only 40 bits per second. Stop thinking so much and you actually think better.
A medicine has an effect on reducing symptoms. It also has a halo of belief-effects or placebo. A non-material cause of a physical event. Your confidence catalyses the belief which increases the likelihood of a favourable outcome.
Its the same reason radical changes in diet work so well. A halo of belief in the new remedy provides the seed of its own fulfilment. I feel so great! That's until the placebo washes off and what's left might not be so impressive.
Self-belief then is a useful tool to bolster performance. Those who are more realistic about the difficulties of a challenge tend to be slower, more distracted and likely to give up. The optimist piggybacks the halo of belief-effects and drives on. It seems there is a place in society for offensive optimism. It's sport.
The conscious brain is Windows 95 installed on a brand new desktop. The desktop or subconscious has far greater capacity for insight if we can uninstall Windows long enough to see its intuition. No experience turns out exactly as it’s laid out in our minds so a realist assessment tends to dissolve on the first note it falls short. It’s lunacy of optimism that serves as the ingredient of its own fulfilment. Perhaps that’s why we tell our kids they can achieve anything they wish. The placebo increases the likelihood that they do.