What a burndown chart actually shows

A burndown chart plots remaining work against a straight-line "ideal" pace from the sprint's total points down to zero. The value isn't the ideal line itself - nobody expects work to burn down in a perfectly straight line - it's the gap between ideal and actual, which is the earliest visible signal that a sprint is off track, days before the standup conversation would surface it on its own.

Reading the shape, not just the endpoint

A flat stretch followed by a steep drop usually means work finished in a batch near the end, not steadily - common, and worth noticing if it happens every sprint (it often means testing or review is backed up until late). A line that's consistently above ideal from day one is a scope or capacity signal worth raising early, not waiting out.

What it doesn't tell you

Burndown only tracks points remaining against a fixed starting total - it can't show scope that got added mid-sprint, because added scope just makes the line look like it stalled instead of showing the real cause. If scope changes mid-sprint are common on your team, a burnup chart shows that directly instead of hiding it.