Why can't Paul talk to his father about the war?

Paul can't talk to his father because he's afraid he won't be able to stop talking, that he'll reveal more than he should. His father wants to share his experience, but Paul knows that what he's been through cannot be shared.

My mother is the only one who asks no questions. Not so my father. He wants me to tell him about the front; he is curious in a way that I find stupid and distressing; I no longer have any real contact with him. There is nothing he likes more than just hearing about it. I realise he does not know that a man cannot talk of such things; I would do it willingly, but it is too dangerous for me to put these things into words. I am afraid they might then become gigantic and I be no longer able to master them. What would become of us if everything that happens out there were quite clear to us?

So I confine myself to telling him a few amusing things. But he wants to know whether I have ever had a hand-to-hand fight. I say "No," and get up and go out