Because everything is impermanent, the satisfaction associated with whatever is reached for is also impermanent and this is the exact reason why one is constantly reaching and remains unsatisfied.
Not being satisfied is so subtle, and how you will know it’s in place is by the next thing reached for. The misunderstanding of the impermanent nature of all things including life itself is what makes one constantly reach for satisfaction. If one knew the reaching wasn’t going to quench the satisfaction, it most likely wouldn’t be done. One reaches for whatever their conditioning deems as needed, and even though it temporarily satisfies the thirst, it doesn’t last and hence the reaching commences. When the impermanent nature of all things begins to be understood, one becomes aware of the nonsense of reaching. This doesn’t mean the reaching will magically end, but one does start to understand the true nature associated with reaching. If there wasn’t the satisfaction associated with food, dessert, drugs, alcohol, gambling, yoga, meditation, ad infinitum, reaching wouldn’t be done. Everyone who reaches for something assumes there’s going to be some sort of satisfaction derived from it. Do you not?
Existence is pretty stable as far as life being life, but the events that occur within life are not. There is constant change in everything, but the mind is mostly blind to this because it wants stability (permanence). It defaults to making you believe the next fix will be it, but I guarantee you the next fix only leads to the one after that and so on. It never ends because there’s nothing permanent that allows it to end. Because everything is impermanent, the satisfaction associated with whatever’s reached for is also impermanent and this is the exact reason why one is constantly reaching and remains unsatisfied.