I dropped into a dark shadow, took a lungful of air and let it out in a howl—the snarling howl of a gray timber wolf, lonely and hungry and far from home, and mean enough for seven kinds of trouble.
For above sentence, the writer uses 'seven kinds of trouble' instead of many kinds of trouble. (I think it is the meaning.)
Is there any reason in English they seem to prefer the number '7' to other numbers? Like seven deadly sins.