Numerical quantities focus on expected values, graphical summaries on unexpected values.

There is no data that can be displayed in a pie chart, that cannot be displayed BETTER in some other type of chart.

An approximate answer to the right problem is worth a good deal more than an exact answer to an approximate problem.

Visualization is often used for evil - twisting insignificant data changes and making them look meaningful. Don't do that crap if you want to be my friend. Present results clearly and honestly. If something isn't working - those reviewing results need to know.

Be approximately right rather than exactly wrong.

It's better to solve the right problem approximately than to solve the wrong problem exactly.

This is my favorite part about analytics: Taking boring flat data and bringing it to life through visualization.