"The sheer frequency, spontaneity and seeming irrelevance of his lies have no precedent. Nixon, Reagan and Clinton were protecting their reputations; Trump seems to lie for the pure joy of it. A whopping 70 percent of Trump's statements that PolitiFact checked during the campaign were false, while only 4 percent were completely true, and 11 percent mostly true."
https://www.politico.com/magazine/story/2017/01/donald-trump-lies-liar-effect-brain-214658