For what it is worth: I had a situation where a client came in complaining about breaking G strings. After throughly checking out the instrument I played it vigoursly and could not break a string. When the client came to pick it up I asked him to play. In very short order he broke the G string. problem: He used a very light pick which totally wrapped around his thumb on the down stroke and he would hook the G string with his thumb and tear it off at the bridge saddle.. I convinced him to use a heavier pick and ease up a little bit. Problem cured.