The quote directly asks you to question your own identity, specifically the mental construct of 'I'. It suggests that this feeling of being an individual, separate self, is a thought that arises and has a source. The instruction is to trace this thought back to its origin.

In the Advaita Vedanta tradition, as expounded by Ramana Maharshi, this is the core of self-inquiry (Atma Vichara). The 'I' thought is seen as the root ignorance, the primal illusion (maya) that veils the true nature of reality. This reality is the Self (Atman), which is identical to Brahman, the ultimate, unchanging consciousness. The 'Self' is not a personal ego but the pure, attributeless awareness that underlies all existence. By relentlessly pursuing the source of the 'I' thought, not as a mental exercise but as a direct, intuitive investigation, one dissolves the ego-construct and realizes the ever-present, non-dual Self. This is the path to liberation (moksha), as described in texts like the Upanishads, which Maharshi so powerfully re-emphasized.

In your life: When you feel a strong emotion or a sense of self, pause and ask, 'Who is feeling this?' or 'Where does this sense of 'I' come from?' without trying to answer intellectually, but by turning your attention inward.