I'm currently studying the building blocks of motivation with temporal motivation theory (TMT) and one of the building block is expectancy, where optimism bias plays an important role.

In evolutionary environments where rewards were highly valuable compared to the costs of fighting for those resources, it is advantageous to have inflated expectancy beliefs to obtain the resources because veridical beliefs may be self-limiting. Without the inflated beliefs, we would not go out for risky hunts, travel to new regions, or try new food resources. In today’s environment, this optimism bias is not as warranted but not necessarily unbeneficial.