There are a bunch of problems around getting the algorithmic newsfeed sample ‘right’, most of which have been discussed at length in the last few years. There are lots of incentives for people (Russians, game developers) to try to manipulate the feed. Using signals of what people seem to want to see risks over-fitting, circularity and filter bubbles. People’s desires change, and they get bored of things, so Facebook has to keep changing the mix to try to reflect that, and this has made it an unreliable partner for everyone from Zynga to newspapers. Facebook has to make subjective judgements about what it seems that people want, and about what metrics seem to capture that, and none of this is static or even in in principle perfectible.