I disagree with this statement, it's not always a poor idea to lie to yourself.
Psychologists call it Optimism bias, the tendency for human beings to generate positive illusions about planned actions and to be overly optimistic about the results of those actions. Every time you buy a lottery ticket or gamble or start a company you are suffering from this bias. You believe that even knowing the odds of failure, somehow you will find a way to make it work — no matter the statistics.
I think that author, Annie Dillard says it best. She says that, “If we listened to our intellect, we’d never have a love affair. We’d never have a friendship. We’d never go into business, because we’d be too cynical. Well, that’s nonsense. You’ve got to jump off cliffs all the time and build your wings on the way down.”
I challenge you to lie to yourself and lie constantly. It’s really the only way to be interesting.