Earlier quoted context omitted.
What in Scrum is about keeping managers happy?
Burn down charts, team velocity, and story points. They all exist to give software development the illusion of predictability, but saying that a project should take “x sprints” is just setting a deadline with extra steps.
The way you get good at estimating is looking at your database of experience. “I did a task similar to this in 8 days”. Calendar time is real and punchclock time is real, either can be measured. Story points are not real and not measurable and they leave you lost at sea thinking that estimation is impossible, a scam, etc.
See also
https://en.wikipedia.org/wiki/Function_point
Which is also a kind of development “funny money” but which have a somewhat rigorous method to arrive at estimates.