In Magic Mountain, one of my favourite novels, Thomas Mann pontificates about the nature of boredom:
A great many false ideas have been spread about the nature of boredom. It is generally believed that by filling time with things new and interesting we can make it “pass,” by which we mean “shorten” it; monotony and emptiness, however, are said to weigh down and hinder its passage. This is not true under all conditions. Emptiness and monotony may stretch a moment or even an hour and make it “boring,” but they can likewise abbreviate and dissolve large, indeed the largest units of time, until they seem nothing at all. Conversely, rich and interesting events are capable of filling time, until hours, even days, are shortened and speed past on wings; whereas on a larger scale, interest lends the passage of time breadth, solidity, and weight, so that years rich in events pass much more slowly than do paltry, bare, featherweight years that are blown before the wind and gone. What people call boredom is actually an abnormal compression of time caused by monotony – uninterrupted uniformity can shrink large spaces of time until the heart falters, terrified to death. When one day is like every other, then all the days are like one, and perfect homogeneity would make the longest life seem very short, as if it had flown by in a twinkling. Habit arises when our sense of time falls asleep, or at least, grows dull; and if the years of youth are experienced slowly, while the later years of life hurtle past at an ever-increasing speed, it must be habit that causes it.