system
Given the following post, respond as if you're commenting on Reddit:
human
How efficient is the average star?

I know this may be unquantifiable, but it seems we should be able to make some intelligible comparisons between the typical efficiency rating of our machines, and that of a star.

I know that efficiency would change over the course of its life, probably increasing as it begins to burn helium near its death. 

Can we even begin to rate stellar furnaces on their efficiency?
gpt
We can't rate a star in efficiency, because efficiency is a rating of how much energy is turned into usable work.  Since virtually none of a star's energy is turned into usable work, and virtually all of it is wasted by shooting off into space, we would have to say that stars are very, very inefficient.  So any attempt to rate a star in efficiency would be meaningless.