Philosopher Dan Dennett makes a compelling argument that not only don't we understand our own consciousness, but that half the time our brains are actively fooling us.
From Wikipedia:
Daniel Clement Dennett (born March 28, 1942)[1][2] is an American philosopher, writer and cognitive scientist whose research centers on the philosophy of mind, philosophy of science and philosophy of biology, particularly as those fields relate to evolutionary biology and cognitive science. He is currently the Co-director of the Center for Cognitive Studies, the Austin B. Fletcher Professor of Philosophy, and a University Professor at Tufts University. Dennett is a firm atheist and secularist, a member of the Secular Coalition for America advisory board,[3] as well as an outspoken supporter of the Brights movement. Dennett is referred to as one of the "Four Horsemen of New Atheism," along with Richard Dawkins, Sam Harris, and Christopher Hitchens
