Counter-intuitive? Not at all. I write magic and dragons and don’t think I have a harder time than a contemporary writer with this issue. If you are writing fiction, you are expected to use a little imagination to bring it to life anyway. I don’t think the old adage is meant to be taken literally. Or rather, you know more than you might think.

• Emotions:
  Whether it is telepathic lizards or werewolves, all characters have
  emotions. Their motivations might deviate from humans, but the
  emotions are still the ones humans have. Humans like you (at least I
  assume). You experience emotions every day so put what you know to
  the page.

• Motives:
  I said non-human characters may have slightly different motives but
  they should still be comprehensible to readers. You know about
  motives from your own experience, talking to and watching others,
  and from reading.

• People:
  You also know how to make multi-demensional characters. The same
  guidelines can be followed when making nonhuman persons and people.
  There might be a few superficial differences (a diet of blood, the
  ability to do magic, or fur and fangs, for instance) but people are
  still people underneath.

• Important
  Issues: You know what issues are important to you. Issues
  have inherent conflict and are well worth tackling in your work.
  Since it is important to you, you should be aware of multiple sides
  to the issue and be able to realistically represent them. From
  bullying to global warming, any core issue can be adapted to your
  fantasy worlds.

• World-building:
  Non-fantasy writers often overlook how much research goes into
  world-building. The land, water, and weather have to align. The
  types of plants and animals need to be reasonable for the climate. A
  cat-creature probably will eat meat, not plants. A snake-creature
  can probably see infra-red.

The
adage “write what you know” should also be expanded to “write
what you can learn”. I justify this modification by the fact that
once you learn something, you know it. Research is probably essential
to any story and fantasy/ paranormal is no exception. Write what you
know, what you knew, and what you will know. Write your heart out.