Some people don't talk much in relationships even when there seems to be plenty to talk about. The silence makes the people who they care about, and who care about them, act just a little bit crazy!
Nagging, persuading, begging, and threatening are a few of the things tried. The motivation: "I want to make them talk to me!"
When that doesn't work, the more verbal person might start talking for both of them, telling the other person how to think or feel. The quieter one may even grow to appreciate not talking. It's more comfortable being told what to think than have to face the discomfort of not having an answer.
That can make the relationship really crazy!
It's common that the quiet person isn't being intentionally obstinate. When they say, "I don't know", it often begs the responding question, "How can you not know? You have to know!" Most of us have participated in this less-than-productive conversation.
What if they are telling you the truth? What if they aren't lying? What if they really don't know?
They don't know why they did what they did or said what they said. They don't know what they want to do. They don't know how they feel or what they think. They don't know.
They don't have words to put with what they're experiencing. They may lack the vocabulary. They may lack the security to speak it.
I was given some great advice years ago, "Kathy, if you want the people you love to talk with you, to trust you, you have the responsibility to be a safe person for them to talk with." After I got over the pride of hearing the truth about myself, it helped. A lot.
Most of us can't tell the difference between being listened to and being loved.
Love well. Listen.