Enlightenment may come suddenly to a man, but then it is usually a temporary glimpse. Only rarely does it stay and never leave him. The normal way is a gradual one. The experience of Ramana Maharshi, Atmananda, and Aurobindo illustrates this rare fated exception, and can only be looked for at the risk of frustration.
-- Notebooks Category 22: Inspiration and the Overself > Chapter 8: Glimpses and Permanent Illumination > # 7