The Facebook profiles of Mark Zuckerberg and his wife Priscilla Chan cannot be blocked because they have reportedly been blocked so many times that the social media giant is stopping it happening.
When people do not want to see your posts, they will either unfriend you, stop following you or they will block you.
If you press the block button on both of their profiles, a message saying "Block Error" will be returned -- meaning that there "was a problem while blocking Mark Zuckerberg or Priscilla Chan" and you should "try again".
Zuckerberg writes a lot about updates to Facebook and news about his personal life or statements on current events on his personal page.
According to a report in The Independent, those posts then seem to benefit from help from the Facebook algorithm and are interacted with, pushing them onto people's news feeds.
Blocking the Facebook founder and his wife was a useful way of keeping those posts from appearing before it was banned.
The ban has been in place since 2010 and even led to a now-defunct website that exists only to point out that it's impossible to block Zuckerberg, the report pointed out.
This is because the site can only allow a person to be blocked a certain number of times and once that limit is reached then they can no more be blocked.