I think it would be tough for polar opposites to maintain a lasting relationship.
True, and we all have had bouts of "the blues" from time to time when we may not be feeling so good about ourselves. I believe that's a normal part of life.
But (for example), someone with chronic low self esteem or someone who always has a poor perception of their own self worth (although it may be a wrong perception) ... would they deliberately hook up with a "basket case" so they won't have to leave their comfort zone?