Plato viewed poetry and other forms of art as imitations of reality. He believed that reality itself is already an imperfect imitation of the ideal Forms, which are the true essence of things. Therefore, art (including poetry), which imitates reality, is an imitation of an imitation.
This view is primarily articulated in his work "The Republic," particularly in Book X, where he argues that poetry and the arts are thrice removed from the truth and can lead people away from knowledge and understanding of the Forms. Because of this, Plato considered poetry to be trivial and potentially harmful to the pursuit of truth and knowledge.