How I Met Your Mother: 10 Biggest Unanswered Questions
4. How Did Tracy Die?
One of the many upsetting plot twists in the show's final season came with the mother's sudden and unexplained death, which in one moment pretty much betrayed everything that Ted's epic tale had been building toward.
The most elusive aspect of Tracy's death, though, lies in the fact that Ted never tells us how she died, and there's not even any clues to rely on for answers. In his flashbacks, Tracy doesn't look ill, she's just seen in a hospital bed.
Of course, Ted's telling his kids the story of their mother, so he probably wouldn't go into too much detail regarding her illness, but not even a passing reference to what was responsible? Like many of the unanswered questions in the show, this one feels extra infuriating given Ted's detail-orientated storytelling.
The show ended with Tracy cruelly written out so Ted could pursue Robin again (sigh), and her cause of death was left painfully ambiguous.