When one tugs at a single thing in nature, he finds it attached to the rest of the world.

These are paraphrases of Muir's quote from My First Summer in the Sierra (1911) - the actual quote is listed above: "When we try to pick out anything by itself, we find it hitched to everything else in the Universe." See Sierra Club explanation.

Tug on anything at all and you'll find it connected to everything else in the universe.