He [Jung] told us that in 1934 he had gone to Bollingen to work and had put up his yellow flag to warn Professor Fierz that he was not “at home.”
He was unable to work, however.
He felt terribly depressed.
A heavy cloud seemed to oppress him.
But he kept his flag up and struggled with the oppression all day Sunday and into Monday.
At last, he pulled down the flag, feeling it was no use trying to work any longer.
Immediately, Professor Fierz came over and told him of the Nazi purge, which had taken place on Sunday morning. ~Esther Harding, Conversations with Jung, Page 13.