[W]hen thinking about difficult, exciting, interesting activities, such as investing in a new business, or perhaps buying a $10 million lottery ticket, the brain areas associated with emotion — such as the midbrain dopamine system — become more active.

Images, colours, music, even social discussion means that the midbrain emotional area becomes dominant, and the rational part of the brain finds it hard to resist the temptation. The emotional centres of the brain simply tell the rational part to shape up or ship out.

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The rational part of the brain agrees, and starts to look for evidence that supports the emotional brain — it becomes an ally in the search for reasons why the emotional choice is a good one.