In Coleridge's "The Rime of the Ancient Mariner," the Mariner has no choice but to tell his tale to the wedding guest that he tells the tale to. The Mariner reveals to the guest:
"Since then, at an uncertain hour,
That agony returns:
And till my ghastly tale is told,
This heart within me burns.
"I pass, like night, from land to land;
I have strange power of speech;
That moment that his face I see,
I know the man that must hear me:
To him my tale I teach. (582-590)
The Mariner just knows, and is in fact forced by the curse to tell his tale to that particular wedding guest.
No information is revealed as to why this particular listener is "chosen" by the curse, he just is. In a poem within which rational thought and linear development is replaced with the imagination and the supernatural, this shouldn't come as a surprise. Rational explanations are not required in a work of imagination.