Some of the quantities are subtle, or we don’t know how to measure them.
There are two in between these two, I think:
* It is measurable, but we won't know what the number will be until after we actually implement and deploy it. For example, "We don't know how many ms, P90, will be saved by switching to QUIC with this client on 3G networks until we try it"
* It is measurable and we know the number, but we don't know what the impact will be until after we implement and deploy it. For example, "We know we'll save 250 ms, P90, by switching to QUIC, but we don't know if that will have a meaningful impact on abandon rate."
