Given to a person, attention is worth the most
Everyone can tell the difference, and nobody mentions it.
The most valuable thing you can do with attention is not a piece of work. It is give it undivided to another person. Everyone can detect the difference between being listened to and being processed while something else runs in the background, and almost nobody says so out loud. The half attended conversation is not remembered as rude. It is remembered as slightly flat, for reasons the other person could not name afterwards.
What makes this significant is that the cost is so low. Twenty minutes of genuine attention is not a large expenditure by any measure, and it is one of the few things that reliably registers with the person receiving it. Most of the relationships that quietly thin out do not do so because of any event. They thin out through a long series of conversations that were attended to at forty percent.
This is also a sensible reason to care about the whole subject in the first place. Protecting attention is easy to frame as a matter of getting more done, which is true and a bit joyless on its own. The wider case is that the same capacity underwrites everything worth having: the work, the reading, the walk, and the person in front of you, who notices whether they have it long before you do.