One of my kids spent a few days in the hospital not long ago. Being in the hospital is stressful, but it is also boring. When your condition is being monitored, there isn't a lot to do. You sit for long periods of time. It is hard to concentrate, which makes it difficult to read, write or even pay attention to the television. Every few hours, somebody comes by and takes your vital signs. Mostly, though, it is a lot of waiting.
While you're there in the hospital, everything feels like it takes forever. The clock ticks slowly forward as you wait and wait and wait. If you look back at a hospital stay, though, it doesn't feel as long in your memory as it did when you were there. How does your perception of time really work?
There is some nice research by Dinah Avni-Babad and Ilana Ritov in the Journal of Experimental Psychology: General from 2003 that addresses this question. They found that people judge the duration of a period of time from memory differently than they judge the duration of a time period as it is going on.
Basically, the busier you are during a time interval, the faster that time interval will feel like it passed. That shouldn't be surprising. We all know that time flies when you're having fun. When you are cognitively busy, you are focused on each task you are performing, and so you don't have the opportunity to notice the passage of time. As a result, the interval feels like it passes quickly. When you are bored, there is not much to occupy your time, and you are much more likely to keep thinking about the time and check the clock. So time feels like it passes slowly when not much is happening.
When you look back on time periods, though, things reverse. How can you decide how long a time period was in retrospect? You have to retrieve events from memory in order to judge durations. When you think back on an interesting time that had lots of new experiences, you are able to retrieve a lot of events from memory. So, interesting time periods feel like they have taken a long time. A trip to a foreign country that felt like it flew by when you were on it feels like a long full and rich experience when you look back on it later.
In contrast, boring time periods do not add much new information to your memory. A day spent in the hospital has few interesting landmarks in memory. Mostly, you're staring at the ceiling and waiting. As a result, when you think back on those boring or routine periods of your life, they will feel like they flew by, even though they were excruciatingly slow at the time.
I guess the mark of a successful life, then, is that the days have flown by, but the years feel long and full.