Encounter
Encounter, from May 1944, and Reptiles are the better-known works Escher produced during the war. He describes Encounter like this*:
Out from the grey surface of a back wall there develops a complicated pattern of white and black figures of little men. And since men who desire to live need at least a floor to walk on, a floor has been designed for them, with a circular gap in the middle so that as much as possible can still be seen of the back wall. In this way they are forced not only to walk in a ring, but also meet each other in the foreground: a white optimist and a black pessimist shaking hands with one another.’
The optimist has his hand open, as a gesture of friendship. The pessimist has his finger raised, as a warning. Yet they shake hands, which lends the print a touch of the encouraging in these times of war.
Source
[*] M.C. Escher, The Graphic Work, TASCHEN, 2001, blz. 11