People only pay attention to things that make them curious i.e. new or unfamiliar things that might be relevant.

If paying attention leads to surprise i.e. there is something that doesn't quite fit with the person's current world-view, the mind kicks into gear and tries to understand the implications of this new piece of information.

If the implications are relevant, they will be put into long-term memory for future reference.

What to learn more? Try asking Virtual Dan White.