Burndown chart vs Burndown mentality

It's no surprise that scrum projects are using Burndown chart for tracking sprint progress and overall product release too.

Burndown chart, as name suggest, keeps burning task/stories as and shows what is still left out.
Every day after, stamp up meeting, is good time spot when we re-draw this chart to reflect previous day's work.

Here is the trap which I have seen many team fall in very easily. While we are using daily stand up to come up with burn DOWN chart, what we are really talking about is how much amount of task have been done (i.e. 4 hours or 1 story point etc). Now truly speaking that information is not really helpful to us. In Agile there is no look back. Whatever happened, does happened. No one in the world can go back and change them. What is important is what to do next. What I mean to say, is we need to start talking in terms of what is left in order to finish this story.

Now, does that sounds like weird argument? One might argue that, isn't that the same information. After all we know total size of the story and by telling what has been done, we can easily figure out what is left. (That's simple math I learned, way back in primary school).

Here is my answer,
My experience with past and present scrum project has taught me the above simple math of deducting completed point from original size is failing too often. While working on story we might encounter more or less complexity than originally anticipated. Which means, for then encountered simple story what is left is too less or for then encountered complex story what is left is much more. And somehow human minds are evolved in such a way that they can give more accurate answer for what is left vs how much is done.

Personally, our charts have improved a lot (in terms of reflating actual picture) when we started forcing team thinking in terms of "what is left" pattern over "what is done".

I call this pattern "BURN DOWN MENTALITY" to update burndown chart.

Thought? comments? arguments? I would love to hear.

Develop smartly :)