Economists and psychologists sometimes speak of temporal discounting: this is the idea that we regard things as less valuable, the longer we have to wait for them.
For instance, if I offered you a donut today, or a donut in a year's time, which would you prefer? In general, wouldn't most people prefer a donut sooner rather than later?
Another way to think about it is that events become more valuable (either more desirable, for good events, or more undesirable, for bad events) the closer they are to the present. A holiday next week is more valuable than a holiday in six months’ time. A visit to the dentist in the next hour is much worse than a visit to the dentist in a few weeks.
In the video below, we show how we can represent these phenomena precisely.