Here's why it's a major complication:
* The Return of the Tribute: The Quarter Quell forces Katniss and Peeta to return to the Games, putting their lives at risk once again.
* Increased Stakes: The Games are more dangerous and brutal than ever, with the introduction of deadly traps and the inclusion of previous victors as tributes.
* The Rebellion's Spark: The Quarter Quell becomes a catalyst for the rebellion against the Capitol, as the Games highlight the injustice and cruelty of the Capitol's system.
* The Threat to Katniss and Peeta: Katniss and Peeta face constant danger, both from the other tributes and from the Capitol's manipulation.
* The Moral Dilemma: Katniss struggles with the moral dilemma of playing the game while secretly trying to inspire rebellion, putting her and Peeta at risk.
The Quarter Quell drastically raises the stakes and sets in motion a chain of events that leads to the full-blown rebellion in the subsequent books.