The same underlying data can be made to look dramatically different depending on how a chart's axis is set: starting the vertical axis at a value other than zero, for instance, can turn a genuinely modest change into a line that appears to shoot sharply upward or downward across the page.
Checking the axis before reacting to the shape of a line is a small habit that catches a surprising number of misleading charts, since the visual impression of a graph often does more to shape a reader's immediate reaction than the actual numbers being plotted along it.
This is not an accusation that every dramatic-looking chart is intentionally deceptive, since compressed axes sometimes genuinely serve a legitimate purpose, but it is a reason to check the numbers directly before letting the shape of a line alone determine how alarmed or reassured to feel. It rewards patience considerably more than it rewards any particular cleverness applied in a single moment.