It was only hours later, looking back on the day as he wrote in his journal, that Ianto realised that he had lied to Jack.
Jack, whom he had sworn, if only to himself, that he would never lie to. And Ianto Jones never broke his word.
So he buried that memory, too.
When he told Jack, later, that he told him everything, Ianto was telling the truth.
So. I like to do things to Ianto and his mind (I'm a horrible person to the characters that I love). I'd like to write a fic, at some point, addressing the revelation of Day Five; I think it has the potential to be very dark and fucked up, but beautiful. For now, googlebrat's Love of the Common People is canon.
I know how easy it can become to edit memories. But things that are long buried can rush out and overwhelm you sometimes.