The big lie is a propaganda technique generally employed when telling the truth would be unfavorable to your side. It goes like this: never admit doing any wrong and instead always insist on a story that portrays your side as the good guys. What really happened is irrelevant. The key is repetition. Do it often enough and loudly enough until most people believe you.
While the big lie is most often associated with authoritarian governments, its use is actually quite widespread. For example, the Montreal Gazette recently published a front page article claiming Jewish students at Concordia University were “feeling like the target of a hate campaign.” The reason cited, as far as this writer can tell, was simply that many students were standing in solidarity with Palestinians.
http://dissidentvoice.org/2015/12/erasing-palestinians-from-their-homeland/