Explain it at four levels until it clicks

Explain {{concept}} at four levels, each complete on its own:

1. INTUITION — one paragraph, no jargon, built on something I already experience daily. Then say precisely where this intuition breaks.
2. MECHANISM — how it actually works, step by step, introducing only the terms that earn their place. Define each on first use.
3. FORMALISM — the precise definition, notation, or model practitioners use, with each symbol explained and a worked example with real numbers.
4. FRONTIER — what's still debated or unknown, and where this concept's usefulness ends.

Then:
- The three misconceptions people hold about this, and what makes each seductive.
- Two questions I should be able to answer if I understood it. Give the answers separately so I can test myself first.
- The neighbouring concept it's most often confused with, and the distinguishing test.