Furthermore, the flaw gives the means for growth brought about by the events of the story and so becomes essential to the plot. The shadow is not the character's evil side, but is a characteristic that has been suppressed because it doesn't easily blend with the other three traits. Give your character a strong central trait that is somewhat stereotypical. Pick something that can be defined in two to four words. For protagonists, this spine will lean toward the admirable.
Villains get a spine that leans toward the despicable.
Edward is a uncompromising corporate raider. Vivian is an honest and upbeat hooker. While these traits create strong conflict between them, they don't give the characters much depth, nor do they provide any basis for their attraction or growth. Although this is partly to comply with the rule that the hero's traits lean toward the admirable, this subtle difference is also proven out by the events in the story. Next, add a supporting trait that's consistent with the spine.