Accidentally killing your Tamagotchi was every kid's (and Tamagotchi-sitting parent's) worst nightmare.
The Tamagotchi was originally released in 1996. Basically, they were portable pets — owners would feed, clean, and play games with them. There was also a social aspect: if two Tamagotchi were near each other, they were able to detect one another (not unlike Snapchat's Snapcodes feature) and visit each other's screens.
While Tamagotchi are still being made, they never recreated the magic they had in the late '90s and early 2000s.