User blog comment:The ASL Pirates/Haoshoku Haki Theory/@comment-4718355-20150220164154

I think it has something to do with, in general, having an enourmous willpower and strength. but at the same time, I think to fully bring out haoshoku, one must exibit a large amount of emotions through anger or a desire to protect. examples: doffy likely awakened his from being tortured by citizens and in the flashback trebol stated everyone passed out. ace awakened his to protect luffy and same with luffy against the gorgon sisters. now for others, such as rayliegh, shanks and whitebeard and chinjao, they were already legendary figures in their life, so going through the new world likely helped them awaken it at some point or met someone to help them awaken it. Now why doffy, who is clearly a pure evil man has it is beyond me, but I'll bet the other yonko possess this haki given their might and strength. Haoshoku likely is given to those who have what I call "the will of the king" and maybe doffy gained it solely because of his insane desire to live and his genuine care for his officers in his crew.
 * now hancock, through her horrors as a slave likely awakened it during her escape when they were almost caught, At least that's what I think. very little is known about her haki skills, but given she's a kuja, she is obviously possibly one of the strongest haki uses in the series. maybe when we see her past someday we'll see what drew out her haki, wouldn't be surprised if her mother was a former empress who died saving her and her sisters at some point. who knows, I wouldn't be surprised if oda revealed she has the initial D. in her name as well in a flashback like Law, but I doubt it.