a mystery to (one)

Something that is difficult to understand. Why she walked out in such a huff this morning is a mystery to me! She was acting normally before that. It was a mystery to scientists where the birds migrated to until they banded some of them and tracked their movement.

Common Names:

Name	Pronounced	Usage
Jimi	JIM-ee	English
Birgitte	-	Danish, Norwegian
Marian	['mɛəriən]
Wilson	WIL-sən	English
Tansy	TAN-zee	English (Rare)
Margaretha	mahr-gah-RE-tah (German)	Dutch, German