This tip is pretty simple to understand if we just put the proverbial shoe on the other foot. Remember that one time when that jerk came flying down the street out of nowhere, totally cut you off and almost caused a huge accident? Don't be that jerk.
Aggressive driving is hard to quantify, but it definitely increases the risk of accidents. Studies show that young male drivers are more likely to drive aggressively [source: NCHRP]. An aggressive driver does more than just violate the tips in this article -- they may intentionally aggravate other drivers, initiate conflict, use rude gestures or language, tailgate or impede other cars, or flash their headlights out of frustration. These behaviors aren't just annoying, they're dangerous.
Defensive driving incorporates the other tips shown here, such as maintaining a safe distance and not speeding, but remaining calm in the face of frustrating traffic issues is another major part of the concept. Accept small delays, such as staying in line behind a slower car instead of abruptly changing lanes. Yield to other cars, even if you technically have the right of way.
Defensive driving is not only safer, it can save you money. Many insurance companies offer discounts to drivers who complete defensive driving courses.