[RaftPeople]

Past experience can be used to drive good estimation. But it takes experience with the process of estimating to know when you "know" that your experience is relevant, and when it's not clear if the previous experience translates.

[bicijay]

It doesn't matter how much experience you have with past estimates if one of the steps in the flow involves a scenario where you just can't estimate it. (Happens a lot when dealing with third parties)

[RaftPeople]

I think for that scenario, there would have to be experience estimating based on the third party involved.

We have third parties building portions of our systems and for some of them I can estimate reasonably well their actual net duration because I've had a lot of experience with them, and they've been fairly consistent.

But there are others where there's a wide range, so I think it boils down to whether you can spot a pattern or not.