The flashbacks showing how Jennifer was broken - her lab was attacked by the Pallid Man, who proceeded to slaughter her coworkers in front of her (complete with loving closeups of each throat being cut) to try to force her to tell where the virus was. He then left her kneeling in front of the dead bodies with the knife in her hands, so when her father found her, he believed she had killed the others and promptly had her committed to a mental asylum. Jesus Christ.
The death of the young girl in Haiti, her pillow drenched in the blood coming from her mouth, and then the shot of her shortly afterwards, her mouth gaping and eyes empty and unseeing.
Poor Athan. So, imagine this: you're a time traveller, and during your travels you meet someone with whom you've fallen head over heels in love. But they die, and you can't imagine life without them. So you travel back to prevent their death... but they still die. So you go back and try again... but they still die. So you go back and try again... and yet again they still die. So you go back and try again...
"The definition of insanity is doing the same thing over and over again and expecting different results." How insane would one be after the six-hundredth attempt?