An actual example I've seen: you can ask a field technician "how long will it take to install this piece of equipment in the field?" and get a pretty good answer. You can't ask a data scientist "how long will it take to build a statistical model to predict how long jobs out in the field will take?" and get anything at all useful.

And you certainly can't ask "how long will it take to build a statistical model to predict how long it'll take a data scientist to build a statistical model?"...