From the Nobel Prize website:
This is the first time I have had to make a speech in front of such a large audience, and I am feeling somewhat apprehensive about it. It is easy to imagine that this sort of thing comes naturally and easily to a writer. But a writer – well, a novelist at least – often has an uneasy relationship with speech. Calling to mind the way school lessons distinguish between the written and the oral, a novelist has more talent for written than oral assignments. He is accustomed to keeping quiet, and if he wants to imbibe an atmosphere, he must blend in with the crowd. He listens to conversations without appearing to, and if he steps in it is always in order to ask some discreet questions so as to improve his understanding of the women and men around him. His speech is hesitant because he is used to crossing out his words. It is true that after several redrafts, his style may be crystal clear. But when he takes the floor, he no longer has any means at his disposal to correct his stumbling speech.
I also belong to a generation in which children were seen and not heard except on certain rare occasions and only after asking permission. But no one ever listened and people would often talk across them. That explains the difficulty that some of us have when speaking – sometimes hesitant, sometimes too fast as if we expect to be interrupted at any moment. This is perhaps why the desire to write came over me, like so many others, at the end of childhood. You hope that the adults will read what you write. That way, they will have to listen to you without interrupting and they will jolly well know what it is you have on your chest.
More here.