Hesech HaDa'as

The fact that there are those who assert that the generation is not worthy for the redemption, etc., is itself a proof that now is the time of the revelation of Moshiach, being that the sages state that Moshiach comes "b'hesech hada'as" -- when we are found in a state like this that neither da'as nor the revealed intellect sees any possibility for the coming of the geulah: this is "hesech ha'da'as" which is a sure sign that the geulah is very close.

Sicha of the Lubavitcher Rebbe, LS 10:171