I  tend to keep numbers in my head a lot so if I see `<X>` number of friends today that okay. But tomorrow or later tonight that number changes to `<X-1>` or `<X+2>`. This also happens alot during the end/start of a semester `<X-15>` or `<X+15>`.

Are my friends just constantly changing their privacy settings or deactivating/reactivating Facebook?  What is the reason for these fluctuations ?