A lot of things complement each other. How one thing cannot function without the other.

Just like a table and a chair. One cannot go without the other. Size matters too. A tall chair won't fit a short table and the other way round.

Just like a lock and a key. Not all keys can open a lock. The little teeth matter.

What is a radio without speakers, a car without wheels, a bed without mattress.

Most importantly, who am I without you.