Crib death, also known as SIDS, is when babies stop breathing and die for unexplainable reasons in their sleep. (theattachedmother.com)
And there's somebody — or something — out there who for some irrational, unexplainable reason is killing us. (religion-online.org)
Also, for some unexplainable reason, attacks are sometimes split up between different monsters instead of concentrating on one foe at a time. (randomnpc.com)