Two cynical explanations spring to mind.<p>1) Those genetically programmed to believe in free will might also genetically programmed to be more optimistic and work harder.<p>2) People who believe in free will have not yet run into their limitations. This would imply that they have not yet run into systemic situations where their energy or mental capacities have been overtasked, meaning they are healthy people who can handle things. This experience, of course, makes them optimistic about their future. They still believe they can accomplish anything they set their mind to.<p>Conversely, it might be that people who do not believe in free will think that way because they have experienced running into the limitations of their own brain and willpower. That is immensely discouraging, which of course dampens optimism. And if they have already hit that brick wall, then they are not so very healthy and in fact are reasonable to be less optimistic about their future and likely to not perform as well as their healthier colleagues.