"Picasso was deeply impressed by Matisse's Goldfish and Pallete, and its emotional force and resonant use of black seem to have influenced his 1915 Harlequin... Harlequin is one of Picasso's first clear images of a divided personality. ...This evocation of multiple identities is given an added dimension by the rendering of... an unfinished canvas. ...Because this rectangle is rendered in a painterly way, it also suggests... the process of painting... a reminder of the impossibility of completeness, either in painting or in life. ...[W]hen Matisse saw Harlequin... he told the dealer that his goldfish had led to it, for in this painting Picasso had picked up precisely those aspects that Matisse had taken from him, such as the conflation of the figure with its surroundings, the suggestion of different psychological viewpoints, the fractured planarity, and... the situating of the picture in a space... somewhere between the thought and the seen, the internal and the external. In Harlequin, Picasso responds with his own version of multiple realities... the strong sense of process and... use of black... to evoke both light and darkness... as lessons from Matisse's painting."
January 1, 1970
https://en.wikiquote.org/wiki/Matisse_and_Picasso