I think, therefore I am is the statement of an intellectual who underrates toothaches. I feel, therefore I am is a truth much more universally valid, and it applies to everything that's alive. My self does not differ substantially from yours in terms of its thought. Many people, few ideas: we all think more or less the same, and we exchange, borrow, steal thoughts from one another. However, when someone steps on my foot, only I feel the pain. The basis of the self is not thought but suffering, which is the most fundamental of all feelings. While it suffers, not even a cat can doubt its unique and uninterchangeable self. In intense suffering the world disappears and each of us is alone with his self. Suffering is the university of egocentrism.