In some trivial sense, we're all doing it constantly. The brain processes a lot of information that doesn't enter your train of thought. Then there's everything we experience but reflexively avoid thinking about due to some fear, pain, or conditioning. Then there's willful "putting out of mind," or willful forgetting, selective attention. And if ya push some of those hard, ya get ritual self-manipulation. I guess I'd argue the most common lie of omission is to the self.