The following is taken from Sadhana Saram, a wonderful text that explains the teachings of Sri Ramana Maharshi written by Sri Sadhu Om, a direct devotee of Sri Ramana’s:
48. The Manner of the Dawn of Knowledge (Janodaya Vidham)
268. Death happens in a split second. Awakening from sleep happens in a split second. Similarly, the destruction of the delusion of individuality happens in just a split second. True knowledge is not something that can be gained and then lost. If a person feels that true knowledge is coming and going, he is still only in the state of practice (or abhyasa). It cannot be said that such a person has attained true Self-knowledge.
The perfect awakening into the state of Self-knowledge happens in just a split second. That state is not attained gradually over a long period of time. All the sadhanas that are practiced over a period of many years are meant only for attaining blemishless maturity.
Listen to an apt illustration. After people have placed gunpowder in the iron barrel of a temple-cannon, after they have added broken pieces of brick, after they have packed it tight with a ramrod, after they have placed a wick in contact with the powder, and after they have plastered the open end of the barrel with clay, as soon as the charge is ignited it will explode in a split second with a blast that sounds like thunder.
Similarly, after one has learnt the truth about the real Self through hearing and reading, after one has practiced sadhana for a long time, after one has wept and prayed with heart-melting devotion, and after one has thereby attained purity of mind, the knowledge of the reality will instantaneously shine forth in a split second as “I am I”. As soon as the dawn of Self-knowledge thus takes place, due to the clear shining of the reality of this state, which is an empty space devoid of objective knowledge, will be spontaneously realized to be the state of true knowledge, which is our beginningless real nature.