Defined por Ink On Paper [Rated T] 

And he interrupts her because he can read her mind –or, at least, is listening to her eyes, "No. I still don't believe in soul-mates." Yin and yang, yes. Pah, yes. Soul-mates, there is no such thing. "We aren't soul-mates, Ziva. Because Thomas and Sayda were soul-mates. Leah and John Mayne were soul-mates. Look at how they ended up." And his logic is, actually, flawless.

I actually clapped my hand to my mouth when I read that part. I never even thought of it.