The bane of all mortal cultivators, Heart Demons were not merely the boogeymen constructed by elders to stress the importance of the Dao Heart, but genuine demonic entities born from the latent desires of all mortal cultivators.
Ancient Lianist scholars believed that the cultivation road had been jointly created by the Lords of Heaven and Hell. That by going through the hurdles of immortal cultivation, cultivators fed Heaven's Will. And by letting their Heart Demons grow, they nourished Hell itself. Solid proof didn't back these beliefs, yet the fact remained that Heart Demons could slowly corrupt careless mortal cultivators and force them into demonization.