Strictly speaking, Daoist doctrine distinguishes between heavenly immortals and earthly immortals. An immortal in heaven can ride on clouds throughout the celestial realm. To ascend to heaven is the highest ideal, but a heavenly immortal can never go back to earth and be among humans. Earthly immortals, on the other hand, can come and go among humans as they please.
道教神仙理論，將修仙層次分為天仙、地仙，天仙一旦羽化登仙，可以翱翔於雲霧飄渺的雲天之上，是道教神仙論的最高理想，但天仙也因此遠隔人間，只能「悶」在雲霧之上的仙鄉奇境。