People love to say, "Oh, the true tragedy of Reid's story is that he turned into Gideon," and that's all well and good. They have a lot of parallels in trauma, with losing partners and agents to bad calls with unsubs. One can point to a parallel of them watching their teams slowly leave the BAU, until the team they started with has nearly disappeared.
But I beg y'all to consider: Hotch and Elle.
She foretells the trauma he would someday incur, showing how one can be pushed to violence. They both have an understanding of the rage that injustices and trauma from their work can morph into violent action, as can be seen in their lines in Season 1, Episode 17, "A Real Rain."
Elle is a warning sign. She is a canary in the coal mine, the first to fall as the BAU continues a cycle of crumbling and rebuilding. She is what happens when they let signs slide, that it would be invasive or profiling a team member to do something about an agent in a mental health crisis. The loop just continues on, and on, and on. Elle, Reid, Gideon, Garcia, Hotch, Emily, Rossi, Morgan, JJ- On and on and on.
So maybe the true tragedy of the BAU is their neglect of the signs and warnings right in front of them, dooming them to an endless cycle of tragedy and trauma.