Leaving a note on the car you dinged is ten seconds of awkward. Driving off is a secret you keep forever.

Two costs, wildly different shapes. One is a short burst of embarrassment, a phone number on a scrap of paper, possibly an awkward call and an insurance claim, and then it is over. The other has no end: you keep walking past that spot, you keep a version of the afternoon nobody else has, and you learn that you are someone who drives off.

Write the note before you have had time to look around. Name, number, what you hit. If it already happened and you can still find the car, a late note is better than none, and easier to explain than you think.