"Clinging to a rock while being battered by waves only causes damage, while letting go and learning to swim freely in the changing waters can result in a great sense of meaning and well-being."
I love this quote and think there are two very basic ideas expressed in it.
First, it is a reminder that the only thing in the Dharma that doesn't change, is change.
The second, is the concept of radical acceptance. Which is simply to accept "what is".
Sounds simple and maybe passive, but it is in fact, neither. You must accept present circumstances, whatever they may be, in in order to facilitate change. There is truth in any given situation. You can accept the truth or you can fight it. Fighting the truth doesn't change it, it simply creates suffering.
We cling to many rocks. Those rocks can be our habits, our expectations, our ideas, politics, and judgements...to name a few. We dwell on things we do to not like and become mired in our reactions and feeling about those situations. To accept a situation is to let let go of the rock, to invite and accept change. That acceptance can be utterly liberating
So let go of the rock. The water is fine.