This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / The Time Traveler's Wife
The cause of Clare's miscarriages: the fetuses are time-traveling out of her body and then being unable to travel back inside safely. One time it travels into the bed next to her and just dies in front of her.
It hangs over Henry and Clare's head why a version of himself older than his 40s has never appeared. It's because he was shot when he traveled back to Clare's house and was shot by her brother and father by accident. He then returns back to his house, family and friends and dies in front of them.
It's arguably worse in the film, as Henry instead skims back to the present, appearing randomly in his house naked, bleeding from the chest and gasping.
Henry temporarily suffering from a condition similar to severe Parkinson's after he takes an untested medicine to control his disorder.
Henry losing both his feet due to frostbite. He screams down a phone at the past version of himself to pick him up, but he arrives too late. Henry loses his most valuable tool to survive when time-traveling.