“Once a King in Narnia, always a King in Narnia. But don't go trying to use the same route twice. Indeed, don't try to get there at all. It'll happen when you're not looking for it. And don't talk too much about it even among yourselves. And don't mention it to anyone else unless you find that they've had adventures of the same sort themselves. What's that? How will you know? Oh, you'll know all right. Odd things, they say-even their looks-will let the secret out. Keep your eyes open. Bless me, what do they teach them at these schools."
-The Professor”