What is Percy Jackson's irritating habit?

Answer 1

Fatal Flaw"To save a friend, you would sacrifice the world."

-Athena, to Percy about his fatal flaw in The Titan's Curse

Percy's fatal flaw was excessive personal loyalty: he would risk the world and even his own life to save a loved one or even a stranger according to Athena. Athena was obviously displeased that her own daughter was an object of that loyalty. Kronos previously exploited this trait in The Lightning Thief, The Sea of Monsters, and The Titan's Curse. Athena also says "The most dangerous flaws are good in moderation" when Percy protests that personal loyalty isn't all that bad. In The Son of Neptune, Mars states to Frank that Percy's flaw would hinder the completion of the Prophecy of Seven, which worries Frank. Hera, however, states that his fatal flaw will keep the seven together.