Hope for the best.
Expect the worst.
The world’s a stage.
We’re unrehearsed.

Mel Brooks (b. 1926) American comedic actor, writer, producer [b. Melvyn Kaminsky]

The Twelve Chairs, “Hope for the Best, Expect the Worst” (1970)
    (Source)

(Source (Audio)). More information on composition of the song here and here.

See also Shakespeare and O'Casey.