How long is the coastline of Britain? It sounds like a question with an answer, until you try to measure it. Use a long ruler and you cut across the bays; use a shorter one and you trace into each inlet, finding more length. Shrink the ruler again and the coastline grows once more. The closer you look, the more detail appears — and the detail looks like the whole.
Benoît Mandelbrot called these shapes fractals: objects whose structure repeats across scales. A branch resembles the tree; a tributary resembles the river; a jagged minute of stock prices resembles a jagged year. Self-similarity is not a curiosity — it is one of the most common signatures of how nature builds, from lungs and blood vessels to lightning and snowflakes.
The pattern is recursion made visible: a simple rule applied to itself, over and over, producing endless complexity from almost nothing. The whole is written into every part.