It's ironically perfect how Hitler wasn't even referring to "the holocaust" in any way with that quote, yet he exposes it for the lie it is unfailingly. The kikes went ahead and proved him right.
Why we believed ?
The fuhrer can answer this question for us :
"... in the big lie there is always a certain force of credibility; because the broad masses of a nation are always more easily corrupted in the deeper strata of their emotional nature than consciously or voluntarily; and thus in the primitive simplicity of their minds they more readily fall victims to the big lie than the small lie, since they themselves often tell small lies in little matters but would be ashamed to resort to large-scale falsehoods. It would never come into their heads to fabricate colossal untruths, and they would not believe that others could have the impudence to distort the truth so infamously