Sometimes people hold a core belief that is very strong. When they are presented with evidence that works against that belief, the new evidence cannot be accepted. It would create a feeling that is extremely uncomfortable, called cognitive dissonance. And because it is so important to protect the core belief, they will rationalize, ignore and even deny anything that doesn't fit in with the core belief.

Actually from a 2008 article on huffpost.com in which the author discusses an explanation given by a therapist friend. The quote has since been attributed to Fanon's Black Skin, White Masks on the internet as well as a few published books, but a google books search shows no examples of books attributing the quote to Fanon prior to 2013, and those that give a specific page number have conflicting information, for example this book attributes it to p. 194 of the 1967 translation of Fanon's book, this book attributes it to p. 119, and this book attributes it to the back cover. A reprint of the 1967 English translation of Black Skin, White Masks can be borrowed on archive.org (the copyright page gives the copyright date as 1967, but at the bottom says this edition is a 1982 reprint), the quote does not appear on any of the claimed page numbers.