Eliezer Yudkowsky, Friendly AI researcher and contributor to the blog Overcoming Bias:

“Never try to deceive yourself, or offer a reason to believe other than probable truth; because even if you come up with an amazing clever reason, it’s more likely that you’ve made a mistake than that you have a reasonable expectation of this being a net benefit in the long run.”

Richard Feynman, Nobel Prize-winning physicist:

“The first principle is that you must not fool yourself – and you are the easiest person to fool.”