I, personally, like to sometimes ship characters with certain traits. For example, I am rather fond of shipping a slightly-unhinged character with a more-or-less sane character (even though both characters could display various traits of mental illness to varying degrees). I feel that it makes for an interesting dynamic, in which the insane character learns from the character better ways on how to cope, while the sane character is drawn into the insane character's world. They learn new things about themselves from each other.
It's almost a Joker/Batman dynamic, somewhat. A tamer variation, and can sometimes lead to the sane character wondering about their own sanity when faced with the insane character's symptoms, particularly if they see themselves in those symptoms.