Things or objects of experience (thoughts, sensations, the body, the world) are changing constantly on their own. Needing them to change implies there is a right and a wrong way for them to be, and creates a resistance to what is.
The resistance is the suffering, not the actual thing itself. It is the very nature of things to keep changing, and resistance to change is the cause of all suffering.
Sometimes the resistance to change is also manifested through a desire for change not to happen. In any case, if you desire one particular manifestation and your happiness and peace depends on it, you will be unhappy and anxious before and after it appears for a brief moment in time.
Ultimately, a desire for things to stay as they are is just as hurtful as a desire for things to change.
Just be, accept, and embrace all of life.