JAY YAROW  – business insider 

Facebook’s News Feed has always been something of a mystery.

Some posts show up in the feed, some don’t. The feed has become over run with all sorts of content and Facebook uses an algorithm to manage it.

But, no algorithm is perfect.

CEO Mark Zuckerberg found this out when the top story in his feed was a co-worker’s birthday. At the same time, his niece had been born.