I think the other responses capture the most important response to your question, which is that we tend to look at the value of things on the margin. However, as you’re clearly thinking intelligently about important ideas, I thought I’d point you in the direction of some further thinking.
Another, perhaps clearer case where this “thinking on the margin” happens is with charity evaluation. If, for example, there existed some very rare and fatal disease which cost only pennies to cure, it would be extremely cost effective for people to donate to an organisation providing cures, until that organisation had enough to cure everyone with the disease. After this point, the cost effectiveness of additional funding would dramatically drop. Usually this doesn’t happen quite so dramatically, but it’s still an important effect. It is this sort of reasoning which has prompted givewell, for example, to look at “room for additional funding”, see here.
There’s another way of looking at your question though, which is to re-phrase it as “how should we assign credit for good outcomes which required multiple actors?”
One approach to answering this version of the question is discussed in depth here. I think you may enjoy it.
I think the other responses capture the most important response to your question, which is that we tend to look at the value of things on the margin. However, as you’re clearly thinking intelligently about important ideas, I thought I’d point you in the direction of some further thinking.
Another, perhaps clearer case where this “thinking on the margin” happens is with charity evaluation. If, for example, there existed some very rare and fatal disease which cost only pennies to cure, it would be extremely cost effective for people to donate to an organisation providing cures, until that organisation had enough to cure everyone with the disease. After this point, the cost effectiveness of additional funding would dramatically drop. Usually this doesn’t happen quite so dramatically, but it’s still an important effect. It is this sort of reasoning which has prompted givewell, for example, to look at “room for additional funding”, see here.
There’s another way of looking at your question though, which is to re-phrase it as “how should we assign credit for good outcomes which required multiple actors?”
One approach to answering this version of the question is discussed in depth here. I think you may enjoy it.