You know what the first rule of flying is? Well, I suppose you do, since you already know what I'm about to say.
I do. But I like to hear you say it.
Love. You can learn all the math in the 'verse, but you take a boat in the air you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps her in the air when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.
~Mal and River, Serenity (movie)