Normally - There Is Nothing Of Which We Are More Certain Than The Feeling Of Our Self - Of Our Own Ego. This Ego Appears To Us As Something Autonomous And Unitary - Marked Off Distinctly From Everything Else. That Such An Appearance Is Deceptive - And That On The Contrary The Ego Is Continued Inwards - Without Any Sharp Delimitation - Into An Unconscious Mental Entity Which We Designate As The Id And For Which It Serves As A Kind Of Façade—this Was A Discovery First Made By Psychoanalytic Research - Which Should Still Have Much More To Tell Us About The Relation Of The Ego To The Id. The Ideas Expressed In The Excerpt Are Most Closely Associated With Which Thinker?