I call it serendipity–the butterfly bush really a weed.  Two years in a row it came up in almost the same spot.  We could see it from our office window.  My wife said it was hard to transplant.  The butterflies loved alighting on its orange flowers.  I did not cut the lawn too well two years in a row.  Our lawn had turned into a meadow and there it was two years in a row.  I considered the plant a gift.  Like manna from heaven.