I see it on here all the time, women defending husbands/DPs usually where posters are saying 'yes but he isn't kind if he yells at you for nothing' or 'He isn't successful if you're paying for everything'.
It reminds me of the 'Selective Attention' theory.
We are primed to not see things that we do not expect we'll ever see. We can not notice things if we've no idea they will be there.
I've dated people who perpetuate lies about more or less everything about them and I've believed it, then with hindsight, the bigger picture comes where you realise they were nothing like what they implied. There's a famous quote, something like 'If you say something loudly enough and often enough, it becomes the truth'.
I've not had a sudden realisation but I have had ones that come up more gradually. I dated an alcoholic once, who lived in a derelict house. He said it was for all different reasons, but when I first met him he had a good job, said his ex had meant he had no time to do up the house, or he'd had to help his parents with money etc etc.
After a time, I realised about the drinking, and that he had no intention of doing the house up and was happy to live in squalor. But I believed him about the reasons originally. Nowadays I would immediately think 'Not relationship material'.
I dated someone more recently who on the surface was great, but I realised more quickly that she was manipulative, conniving, and her personality was entirely made-up!