When avocado prices spike after a frost in Mexico, that's a shift — the supply curve moved because a non-price factor (weather) changed how much can be produced at any given price. When avocado prices spike because everyone saw the same guacamole reel on the same Saturday and suddenly every household wants avocados, that's demand moving — but whether it's a movement or a shift depends on what's driving it. Here's the core distinction: a <b>movement along a curve</b> happens when the price itself changes and buyers or sellers respond. A <b>shift of the curve</b> happens when something other than price changes — income, tastes, input costs, the number of sellers — and the whole relationship between price and quantity gets redrawn.

Supply works the same way. Say you run a food truck. Your ingredient costs start rising — cooking oil, packaging, produce. You can't produce the same meals at the old prices anymore. Your whole cost structure changed. That's a <b>supply shift</b> — the curve moves left, meaning you supply less at every price. A competitor two blocks over raises prices this weekend because there's a food festival and the crowds showed up. That's a <b>movement along the supply curve</b> — higher prices are drawing out more supply from whoever's already in the game. If you're the food truck owner, you'd make radically different long-term decisions based on which one it is. A shift means your business model needs rethinking. A movement means you wait it out.

The non-price factors that shift curves have names — economists call them 'determinants of supply and demand' — but the list is less important than the logic. For demand, they're things like income, tastes, prices of related goods, and expectations about the future. For supply, they're input costs, technology, number of producers, and government policy. When any of those change, the whole curve relocates. Every price on the axis now corresponds to a different quantity than before. The market has to find a new equilibrium from scratch. When price alone changes, nobody relocates. You just move to where you already were headed on the same curve.