Impermanence is the nature of everything that we see, hear, and think. If you take some time to observe the things in your life, you will notice that day by day, hour by hour, minute by minute, and even second by second, everything is changing. Impermanence is not something new, nor was it created by someone. Instead it is a quality of life. It cannot be denied that to exist is to change.
It is hard to believe that everything that surrounds us never remains even for a second. We may see things such as a cars and flowing rivers and they might seem to be the same as the day before, but in reality these things are changing in each and every moment. There are two levels of impermanence: (1) gross impermanence and (2) subtle impermanence. Gross impermanence is something that is not so difficult to understand since it is easily observed. For instance, when we drop a glass and it breaks, this is an example of gross impermanence. Also, suppose someone plants a seed and week by week we can observe the change as the seed sprouts and grows eventually into a tall tree. When we look at this tree we might say things like, "I planted that tree," but obviously the old tree looks very different to the seed that was planted! The change is undeniable - it is right in front of us to look at and judge. The second type of impermanence, subtle impermanence, is very subtle and harder for us to notice. It refers to the minute changes that occur moment by moment that we don't notice, but which are actually the foundation for gross impermanence. Examples of subtle impermanence include the subtle movement of our minds, our aging in every moment, or even the flowing of a river. When we swim in a particular river one year, and then we come back to swim in that same river the next year, we may think and say, “Last year I swam in this river.” However, when we really start to think deeply, the river we swam in last year is gone. In fact even the river you swim in during the morning is not the same as the river you swim in during the afternoon, and actually the river is changing every second!
Impermanence is inseparable from everything. We cannot take things for granted because nothing is predictable. For instance, today someone could be your friend, but tomorrow they could be your worst enemy. Also, your worst enemy may in the future become your best friend. We cannot really be sure about what is going to happen next because it is all impermanent and subject to change. Moreover, rebirth, old age, sickness, and death are part of this changing process. To sum up, there is nothing in this universe which is not impermanent, and indeed it is the nature of everything.