There are four marks of existence—fundamental characteristics that describe the nature of all conditioned reality. They are not beliefs to be accepted blindly, but observations to be tested in experience.
The first is impermanence. Many things appear permanent, as though they will last. But everything eventually changes and passes into another form. Nothing lasts, nothing is reliable; in the end, everything fails.
The second mark is unsatisfactoriness. Reality is filled with a sense that nothing fully satisfies. We think the next purchase, the next achievement, will bring lasting contentment, but it never does. Satisfaction is a fleeting feeling that soon passes. Nothing in this life gives enduring satisfaction.
The third mark is that existence is without essence. The universe and all things in it have no fixed, independent substance. Nothing is truly solid; all is events and flux. That includes ourselves. We do not have a solid, unchanging soul.
The fourth mark is interdependence. The entire matrix of the universe is an interconnected whole. Every part affects every other, like a web: pull one thread, and another part is affected. Nothing is isolated, nothing completely independent. Everything is interdependent.