it is my understanding that line break is usually caused by, as you say, sustained strain on it.. but.. to me any way....
if the line breaks during the retrieval then that tells me one of a couple of things..
one, abrasion on the line causing a weak point..
two.. defective line from the manufacturer and
three OLD LINE..
what would ya'll would say is a reasonable time to keep line (how many months before you replace it).. or a better way to put it is how often should one replace their line ... ??
MacFly ...."May the holes in your net be no larger than the fish in it. ~Irish Blessing"