Charts are charts, right? Wrong.
You have a lot of decisions to make when creating a chart, most of which seem benign. But some of those decisions can make a critical difference between providing insight into the underlying data and causing the reader to draw the wrong conclusions.
To illustrate just three of the ways charts can be made to be misleading, check out Ravi Parikh post on How to Lie with Data Visualization over at Heap's Data Blog.