There have been two mysteries throughout Big Little Lies — who died on Trivia Night, and who was responsible for his or her death. FINALE AND BOOK SPOILERS AHEAD: It wasn't a major surprise when Perry turned out to be the deceased after it was revealed that he's both Jane's rapist and a domestic abuser — my personal prediction was that Madeline would kill him because she's known for both her hot temper and her fierce protectiveness of her friends. So, it was a surprising but brilliant twist when Bonnie killed Perry on Big Little Lies after witnessing him beat Celeste on the balcony as Madeline, Jane, and Renata desperately attempted to fight him off. But, why did Bonnie kill Perry on Big Little Lies?
Throughout the television series, Bonnie has been presented as the most even-tempered, calm, and peaceful character. So the fact that she's the person who ultimately snapped and shoved Perry to his death speaks to just how horrific it is to even witness this level of violence. Bonnie sensed something was wrong earlier in the evening when, from afar, she saw Perry and Celeste arguing — and she seemingly picked up on the fact that this wasn't a typical spat between spouses. Although it wasn't explained on the series, the book elaborated on exactly why Bonnie picked up on every clue and couldn't bear to watch Perry abuse Celeste for another moment.
In the aftermath, Nathan explains that Bonnie grew up in a household where domestic violence was a matter of course — so it revealed the larger issue that this type of abuse is far more prevalent than we'd like to think because it's considered so taboo to talk about. Bonnie's comment to Ed that "everyone has baggage" earlier in the season now makes a whole lot more sense, although I wish showrunners had elaborated a bit more for viewers who haven't read the book.
In a community that's filled with competition (especially between Madeline and Bonnie), one of the highlights of the finale was that everyone on the balcony put aside their differences and came together to protect Bonnie. It showed that, despite all the conflict and disagreement between that unfolded between these characters throughout the series, they ultimately have good intentions and have each other's backs when it all comes down to it. As Bonnie said, everyone has baggage — and, on Trivia Night, so many secrets were spilled and it lead to a display of compassion, understanding, and loyalty.
Celeste was too ashamed and terrified to tell anyone about Perry's abuse, and Jane only confided in Madeline and Celeste about her rape for similar reasons. As the finale proved, shattering the silence was key to bringing everyone together — and it showed that people are often far more compassionate than we might expect.