My interpretation of the quote is that any event in nature, including thoughts and beliefs and walruses and planets and black holes, only exists to the observer as an appearance. What it “is” can only be how it appears, which varies from one observing mind/apparatus to another.
I have noticed that I attach to people and experiences and have a hard time letting them go or more accurately I fear the loss in the present moment.
Feelings of loss and grief do happen, don't they.
Especially for people for whom feelings of strong attachment happen.
The world would be better off, I suspect, if more people did have those feelings.
But since there is nobody with control over whatever is happening or will happen, worry and anxiety are counter-productive and toxic emotions. May a growing acceptance of events bring you peace of mind and body, and less noise disturbing your ability to see and navigate through the whole changing context of your life in any given now.