Situations on the trail are always temporary.
Enjoying good weather? Sooner or later it will turn bad.
Is the trail smooth and easy? Just wait. It will get rocky and steep before long.
The point here isn't pessimism. The trail has a way of reminding you that when things are going well, you should enjoy the moment and take advantage of it.
Conversely, when things are going badly, hang in there. The bad can’t stay that way forever.