Make the insight impossible to miss
A table of numbers hides its story; a good chart tells it at a glance. Visualization is how the result of data analysis reaches people who must decide something. The craft is choosing the right form — a line for trends, a bar for comparisons, a scatter for relationships — and then stripping away everything that distracts from the point.
It is equal parts statistics and design: honest scales and encodings on one side, clarity and restraint on the other. Done badly, a chart misleads as easily as it informs, which is why good practice treats visualization as an argument that must be fair.