"The illusory truth effect (also known as the illusion of truth effect, validity effect, truth effect, or the reiteration effect) is the tendency to believe false information to be correct after repeated exposure." [0]
And even if that's not another boring propaganda operation, what would you be telling if you went to fight on Russian side and got captured by the Ukrainians? "Please, please, please don't hurt me, they made me do it, I went to Russia to do sports and they send me to the frontline".
[0] https://en.wikipedia.org/wiki/Illusory_truth_effect
