Catfish in the fish tank

Back in the old days they tried to ship codfish from the west coast to the east cost and it always arrived mushy. So, they tried sending live codfish and they arrived dead. So they sent the mortal enemy of codfish: catfish, in the same tank. The codfish arrived alive because they spent the entire trip trying to swim away from the catfish. So often we wonder why God put a catfish in our tank: someone we don't like at work, our neighborhood, our family, or our health. He does this to keep you on your toes. To keep you challenged. To keep you alert. So you don't become complacent in paradise and die of boredom.