Gini Impurity: The Blindfolded Archer Who Taught Decision Trees How to Split

Imagine an archer shooting arrows blindfolded at a target. If the target is all one color, any hit is 'correct.' But if it's half red and half blue, the archer has a 50% chance of being 'wrong' no matter what. This probability of being wrong is exactly what Gini impurity measures — and it's how decision trees decide where to split.