間違い
まちがい · machigai · JLPT N3 · noun
mistake
間 (gap, between) + 違い (difference) = a mistake; sounds like match a guy
違い comes from 違う (chigau, to differ or be wrong). Put 間 (ma) in front and you get machigai: something that came out different from what it should be. Saying it as match-a-guy, then getting the wrong guy, is one more way to recall it.