Grief

Grief was an emotion.

In response to negative emotions such as fear, grief and anger, humans once took medication in the future, to remove and override them. (AUDIO: Harvest of the Sycorax)

When the Emojibots first encountered grief, they considered it an enemy of happiness and thought of destroying it, they called upon the Vardy to kill anyone who wasn't happy, stripping them of skin, organs and muscle leaving behind their skeleton, which later would be used to make calcium-based fertiliser. (TV: Smile)