No other life-form on the planet knows negativity, only humans, just as no other life-form violates and poisons the Earth that sustains it. Have you ever seen an unhappy flower or a stressed oak tree? Have you come across a depressed dolphin, a frog that has a problem with self-esteem, a cat that cannot relax, or a bird that carries hatred and resentment? The only animals that may occasionally experience something akin to negativity or show signs of neurotic behavior are those that live in close contact with humans and so link into the human mind and its insanity.
— Eckhart Tolle