There are a few moments in life in which you can always remember where you were and who you were with. These moments can be happy or sad — the brain doesn’t seem to care. As long as the time is significant, there will always be a spot for it in your memory.
For any Brit over the age of 30, an example of this would be Princess Diana’s death; for an American of an older generation, it could be the moon landing.
Although these particular moments have no real significance on your day-to-day, the brain chooses to remember not only the event but also the minor details surrounding it, such as your location and emotions.