One-liner
An inflation index is a basket of prices meant to show, broadly, how the cost of living is moving for the population. It is basically an average, and it does not match anyone's real, personal inflation.
Why it matters
Someone told inflation was mild will disagree if they drive a lot and watched fuel prices jump on war headlines this year. The headline is the average; your inflation is your own basket.
Analogy
Two households reading the same headline can live in different worlds: the one that mostly pays rent and the one that mostly buys fuel feel completely different numbers.
The catch
Taking the headline number as your number. Your personal inflation depends on what you actually buy, and it can run well above or below the index.