by heart
Having got to know Liska the way a man gets to know a woman only if he lives with her for years, sleeping with her all that time – well, he’s got not to know her again. It’s like reading a wonderful poem, and learning it off by heart because you like it so much and you want to be able to recite the whole thing. And when you do know it off by heart you can slowly begin to forget it again. Which is what people generally do.