When we begin our day, we think that everything will turn out as usual, the same as yesterday and the day before yesterday. In this way, we take our lives for granted, and this becomes the condition for much future unhappiness and sadness.
In reality, change is all around us, and even though we don't notice it, things are changing in both gross and subtle ways. Impermanence is unstoppable.
We might believe that friendships will last for a long time, but as time goes on, people change, as do we also change. So it makes sense to expect that our relationships will change. We have to learn to let go of hard feelings and to settle into and make ourselves comfortable in new situations. It is like moving into and getting comfortable in a new house. We have to accept change and learn to make good use of changing situations. When we make space for changes, we can make space to be happy and comfortable in a new environment.