Check out the hypothetical agile burndown and EVM (Earned Value Management) charts below. Like in the “real” world, the example project (or sprint, if you prefer) ended up being underestimated. The shortfall is indicated by the dotted line on the right.
When we literally flip the agile burndown chart in the vertical dimension, we get this:
The moral of the story is: “Don’t be fooled by the agilista herd; an agile burndown chart is nothing but an inverted version of the despised EVM chart.”