"I'm a slow learner, it's true, but I do learn." Sansa had said those words to Baelish shortly before she'd had him executed by Arya's hand and they are words she holds close to her heart. She'd let Baelish and Cersei poison her, trick her into thinking one thing when she should have thought another and she has trouble trusting people now because of it.

Sansa is good at courtesies, of course. She has no issues with being kind and having surface conversations, not really, but when it comes to exchanging truths or revealing something that could be leveraged against her? She holds these things close to her so they cannot be revealed and stolen.

"I learned quite a bit from my cruel tutors."