I found some interesting thoughts in the book Learned Optimism about the evolutionary usefulness of pessimism:

The benefits of pessimism may have arisen during our recent evolutionary history. We are animals of the Pleistocene, the epoch of the ice ages. Our emotional makeup has most recently been shaped by one hundred thousand years of climactic catastrophe: waves of cold and heat; drought and flood; plenty and sudden famine. Those of our ancestors who survived the Pleis- tocene may have done so because they had the capacity to worry incessantly about the future, to see sunny days as mere prelude to a harsh winter, to brood. We have inherited these ancestors' brains and therefore their ca- pacity to see the cloud rather than the silver lining.

...

Pessimism produces inertia rather than activity in the face of setbacks.

If the weather is very cold and your brain's probability estimate of finding any game in the frost is low, maybe inactivity really is the best approach. But if I, as a modern human, am not calorie-constrained, then inactivity seems less wise.