‘Cogito ergo sum’ is a famous statement that asserts the only true knowledge we have is the existence of our own consciousness. Do you think this is really the only true knowledge that you have? Can we ever be sure that the experiential world is not an illusion? Does it matter? Why?

IMO, human knowledge is quite wider than self-consciousness and consciousness of the sensations.
On the other hand, all subjective experiences matter since we need not only to live and know but also find meaning and purpose in life.