'I exist' is the only permanent self-evident experience of everyone. Nothing else is so self-evident as 'I am'. What people call self-evident, that is, the experience they get through the senses, is far from self-evident. The Self alone is that. So to do self-enquiry and be that 'I am' is the only thing to do. 'I am' is reality. I am this or that is unreal. 'I am' is truth, another name for Self.
(Source: ‘Be As You Are’ The Teachings of Sri Ramana Maharshi, Edited by David Godman)