There’s nothing wrong with the way the body grows old and
gets sick. It just follows its nature. So it’s not the body that
causes us suffering, but our own wrong thinking. When we see the right wrongly, there’s bound to be confusion.
It’s like the water of a river. It naturally flows downhill. It
never flows uphill. That’s its nature. If we were to go and stand on the bank of a river, and seeing the water flowing swiftly down its course, foolishly want it to flow back uphill, we would suffer. We would suffer because of our wrong view, our thinking “against the stream.” If we had right view, we would see that the water must flow downhill. Until we realize and accept this fact, we will always be agitated and never find peace of mind. The river that must flow downhill is like our body. It passes through youth, old age and finally dies. Don’t let us go wishing it were otherwise. It’s not something we have the power to remedy. Don’t go against the stream!
~A Tree in a Forest - A Collection of Ajahn Chah's Similes ~