"Whenever feeling downcast, each person should vitally remember, 'For my sake, the entire world was created.'" -- atributed to Baal Shem Tov (Israel ben Eliezer -- b. ca. 1698, d. 1760)
[I said "attributed to" on account of this caveat in Wikipedia: "Israel ben Eliezer left no books [...] Therefore, the most reliable record of his teachings is in his utterances as recorded in the works of his disciples (Hasidim). [...] But since Hasidism, immediately after the death of its founder, was divided into various parties, each claiming for itself the authority of Besht, the utmost of caution is necessary for judging as to the authenticity of utterances ascribed to Besht." Caveat to the caveat: all I know about Baal Shem Tov is from that Wikipedia page.]
To my friends celebrating Rosh Hashanah tonight to Sunday, shanah tovah!