To focus on them is to abort your further thinking, to end up thinking about nothing. Well, only in a manner of speaking. You have to learn how to spot them in order to avoid focusing on them, to keep your thinking focused on existence. A unicorn is like a horse, but is not a horse. A hole is a place without matter.
Darkness is the absence of light.
These negations are red flags of warning not to treat such terms as important, not to focus on them except incidentally and in a manner of speaking. Negative terms lead your thinking down blind alleys to dead ends. Answer yes, and plunge the world into centuries of mystical blight. Answer yes, and end up a pessimist. Answer yes, and end up a skeptic.