Ramana Maharshi - Just as a man would dive in order to get something that had fallen into the water, so one should dive into oneself with a keen, one-pointed mind, controlling speech and breath, and find the place whence the ‘I’ originates. The only enquiry leading to Self-realisation is seeking the source of the word ‘I’.
Meditation on ‘I am not this; I am that’ may be an aid to enquiry but it cannot be the enquiry. If one enquires ‘Who am I?’ within the mind, the individual ‘I’ falls down abashed as soon as one reaches the Heart and immediately Reality manifests itself spontaneously as ‘I-I’. Although it reveals itself as ‘I’, it is not the ego but the perfect Being, the Absolute Self