Time is comprehensible to us as long as we can track it in terms of seconds, minutes, hours, days, and years, but once we go beyond the realm of our own time experience, our perception tends to get fairly vague. For example if I were to ask when Napoleon [1769-1821] was born, I would be lucky to get an answer like "sometime in the middle of the 18th century". We basically have trouble to visualize time intervals that are significantly larger than our own lifespan.