When thinking about the present, most people, including myself, tend to have the “this moment will pass” mentality. By this I mean that they never think of the present moment, they just think that the present moment will pass, and this switches their minds to the future. When going through some tough times, people logically think about when those times will pass, as understandably enough nobody likes going through tough times; if not they wouldn't be tough times. On the other hand, when someone is having a good time, apart from their mind making it seem as time is going by faster, they are constantly thinking about how long it will last, and thus have their minds on the future again. It seems to be inevitable, and even though one would think of it as something easy, living in the moment is one of the hardest things for people to do.
When someone ‘drifts off’ and starts thinking about the future, but at the same time his mind is still somewhat present on what is going on in real-time, time seems to go by much faster. “It is thought that if the brain is busy focusing on many aspects of a task, then it has to spread its resources thinly, and pays less heed to time passing.” (BBC News). This is also the reason behind the saying “time flies when you’re having fun.” And that, along with the fact that people are already anticipating the future, produces the feeling of “time flying by.” That is why, the more busy your life is, the faster it seems to pass by, and that is also why if you stay staring at a clock for a while time seems to go really slowly.
TIme is a complicated subject. It can be affected by gravity, making it go slower or faster, or by our minds, making it seem as if it is going slower or faster. When people think about the future, what comes next, it triggers a reaction in the mind that makes time seem to go faster. People tend to drift off and think about what comes next a lot; during good times and during bad (even though it seems a little bit cliché), either to try and get through tough times, or to figure out how much the good times will last. I have found that the imagination and the neurons can also change the perception of time, and since what we perceive becomes our reality, I guess Einstein wasn’t completely right after all.