Mostly fear I think. A foreboding sense of having made it past their due date and knowing they are on borrowed time. Every day can become their last. I have begun to feel it. Not in a morose way but a realization of the facts of life and death. There is so much left you want to do and so much you are not able to do. Knowing it is likely that an oak you plant will be for someone else to sit in its shade. Bittersweet. Also knowing how quickly you and your planting it will be forgotten as you have seen happen to so many others.
You should be able to understand this intellectually if not emotionally.
Lot of wisdom in what you say.
That is a very valid point.