In a field of arums, there are always some with spots. This means that among a large number of individuals or in a community, there is always one who causes trouble or behaves badly, in other words, the black sheep. It is a reminder that even in the most united and well-intentioned groups, there can be disruptive elements or dishonest people. The equivalent English proverb would be: ‘There’s a black sheep in every flock.’