system
Given the following post, respond as if you're commenting on Reddit:
human
[Mass Effect] Why do the Reapers harvest all sentient life every fifty thousand years?
gpt
It's not *all* sentient life, just the ones that have reached a certain level of technological advancement.  

According to the Reapers, they do this to prevent organics from creating AI that will start a robotic revolution and kill all organic life.