Time is one hell of a tricky business. Some days, it passes like a rocket; other times, it feels like someone put the world on hold. In order to find out more about our ever-changing perception of time and the games it plays with our mind, Bored Panda reached out to Nancy Darling, a professor and chair at the Department of Psychology at Oberlin College and the editor-in-chief of the Journal of Adolescence.

Nancy explained that people tend to judge the passage of time as a function of how many things happen. “I find it interesting that when my days are packed, I feel time passes both very fast and very slow.”

She gave an example: “During a busy week, events a week ago seem in the far, distant past because so many things have intervened since.” Simultaneously, we feel like time is flying by because so many things are happening every hour. Not only is our perception of time purely subjective, it’s also somehow both slow and fast at the same time.

The professor also said that as we get older, the way we perceive time tends to change. It has to do with the usual things, “like cooking a meal or grocery shopping, that start taking longer for you to do.”

Most importantly, “the passage of time just marks age and accomplishment,” according to Nancy. “I just got an email this morning reminding me I’d promised to do something in July. That seems both forever ago (I’ve done a thousand things since) and very close (every day, I keep saying I’ll do it ’tomorrow.’)”

Interestingly, we can do that with life as well. Just think of your kids being tiny and dependent, urges the professor. “How can my son be living in Manhattan and getting ready to teach in the public schools? Time flies,” she said. At the same time, Nancy said that she feels like “there are many things I’d always planned to do, but haven’t gotten to (yet).” And she added: “I am too old now?”

At this point, it’s very important to realize that revising and looking back at our dreams and plans are crucial in keeping time on our side. “If you regularly review what your priorities are and focus on those, you feel like a lot has gotten done and you don’t regret the fact that you’ve wasted your days,” suggests the professor.

It’s all because we need to create a sense of accomplishment, whether big or small, that creates invisible gaps in time. “Days when I accomplish a lot are full and satisfying, but also feel long. A productive week feels like it’s lasted forever. It also feels good,” Nancy concluded. And if time starts feeling longer, it kinda goes slower. Isn’t this exactly the way to stop the clock?

Read more about Nancy Darling’s advice on keeping regular schedules and reviewing your goals in order to make it easier to mark the passage of time in her articles for Psychology Today here and here.