Richard is partly correct in his advice however a guy to me that is a challenge and very interesting for me to know was my ex,
His conversation on many levels ie religion he was a atheist and im wiccan.Conversation is a big plus to me i dont like suck up guys or mama's boys. Sexual banter is great if it makes me laugh and the guy doesnt try to get heavy to fast, his views on the world are a great challenge his expertise in the bedroom can also been seen as a challenge, to some girls even trying to change a homosexual to a straight guy is seen as a challenge sad but true.
Ask her why she see's you as a challenge, then by knowing you have the challenge of keeping it going.
Nothing is more interesting then a challenging partner it adds spice and fun to a relationship but the challenge differs for most females
A mistake is always forgivable, rarely excusable and always unacceptable.
Robert Fripp