Such people are the absolute master/mistresses of that. At 50, I still constantly doubt myself, because of how my own mother is and always has been (gaslighting is a new term to me, but sums up so very well what she does).
Recently she tripped up in a letter to me. After being incensed at what she wrote, I was actually delighted by it - because she showed her true colours!
Truth is indeed so very hard to work out with narcissists and psychopaths...