The truth is—and we all know it from our own experience—all things change.
Whatever we have will change.
The flower blooms and withers. Even our steel automobiles fall to rust and ruin over time.
So if our happiness is dependent upon possessing things, any thing, we're setting ourselves up for the sadness that will naturally come when those things change and leave us.
Wouldn't it be better to discover the source of happiness inside ourselves, so we are not caught endlessly grasping at things that can never give us lasting happiness?