We all know about Percy and Annabeth's fatal flaws but the books don't mention the other seven's fatal flaws. Do you have any thoughts on what they could be?
Alright, I'm going to have a go at this, and if Ginny wants to add she totally can.
Piper- Confidence. I see her flaw being very similar to Annabeth's although she would fall more to over confidence rather than to pride. A huge story arc of hers through the series was her struggling to overcome her self doubt and take pride in who she is. Like all fatal flaws, they are good in small amounts. Having confidence is a good thing, but it can be a problem when you think you can single handedly take on an army.
Leo- Arrogance. Hear me out on this one, because I almost made it insecurity. I believe that if Leo had remained in the same character arc that he was given in TLH (trying to find his place, learning what a home was) he would struggle with insecurity. However, RR totally screwed him over writing wise, and he turned into a womanizing, over the top, cocky jerk. He has a bit of what I call a "special snowflake" syndrome, where he thinks he is above everyone else around him (thinking he is smarter, coming up with dangerous plans and not telling his friends about them, etc). I could easily see him causing his own downfall because he was too arrogant to see the flaws.
Frank- Trusting others. I know that totally doesn't sound like a flaw, but it could have very easily killed him when he trusted Hazel to take his stick for him. He literally has to put his life in the palm of someone else's hands. I think trusting people is very dangerous for him. (Again, super good in small amounts. Disastrous if he puts his trust in the wrong person).
Jason- Lack of self identity. I really do like the way his character arc ended, with him floating between the two camps. However, long distance and constant traveling puts major strain on a person and their relationships. His future could easily be a tragic one- he unties the camps and helps to recognize the minor gods, but at the cost of all the relationships and security he could have had at one camp. (Not to mention what would happen if the camps started fighting again- where would he go? He doesn't have a side to pick).
Hazel- She has no flaws, tbh. (But if I gave her a flaw it would probably be something related to her becoming way too powerful with the mist and it going to her head leading to her downfall BUT it's Hazel and that would never happen).