What would cause a front tranny seal to blow?

There could be a grove on the shaft,or the seal was installed and someone forgot to put a little grease on the convertor snout and she burn out.That does suck.Lucky tho if she pop at say second gear shift you would of went into the wall.Glad it happened at the end.pull it out and have a good look at the input shaft after the seal is out.could also be the big pump seal.