Is it easier to convince a realist to embrace idealism, or a idealist to embrace realism?

it's far harder to convince an idealist to embrace reality. they seem to be constituted in such a way as to deny the facts in front of their face. I think that's why so many of them think that socialism can work even tho it has failed everywhere it's been attempted, and it's even been attempted in Russia, for whoever that idiot was who thought it hadn't