The updating needn't necessarily be instant, it can take months or years. For me, it is never an instant change. Not much "wait, what?!", it's rather more like "this can't be true, let's try to find a counter-argument", followed by "I can't find a satisfactory counterargument, so there may be some merit in that" after some time gap. But after that, I am able to see that I don't anymore hold a belief X which I was ready to defend fiercely a while ago.