system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do we get cranky when we are tired?
gpt
We get cranky because evaluating our responses to stimuli takes energy, which our brain doesn't want to use, so we just spout off. And our brains also turn off reward hormones, because it doesn't want to be tired. So you're not getting endorphine boosts.