The power of chance. I planted the blue-flowered Columbine (Aquilegia vulgaris) in my father's back garden a few years ago and it didn't seem to thrive, getting swamped by other plants. This year it has stood tall and held its own among the frothy white flowers of Cow Parsley (Anthriscus sylvestris) which self-seeds prolifically.
 I didn't exactly plan this delightful combination, but I've noticed that if you plant things in spots that correspond to their natural habitats they tend to sort themselves out over time.