Life a continuous cycle of expansion and contraction

Life consists of cycles that allow for growth and rest. We usually follow that rhythm unconsciously.
It manifests itself in the succession of the night and the day time, or in the cyclic succession of ebb and flow.
We usually use the day to wander the earth for different purposes and the night to rest.
We can't maintain a fixed state for eternity. Civilizations rise, thrive and dissolve to allow others to be born from their embers.
There is no fixity to things. Sometimes we try to freeze pleasurable moments and prolong them, doing ourselves a huge disservice in the process.
Relationships could be a good illustration of that.
Life is changing. It is inherently unstable and wavering, and it wants us to flow with it and to have faith in its workings and bountiful supply.
When we fret, agonize, and resist in our vain attempts to get a semblance of security, we get misaligned with the ever-flowing source of wealth, health ad happiness.

Sicknesses, for example, are speed bumps that get strewn about our life path.

They are meant to slow us down and allow our body and mind to recover and recoup from all the strife and friction we submit ourselves to. 

Health and sickness make up one of the most important expansion and contraction life cycles.