[jefc1111]

Maybe you are getting good quality requirements and / or have a system to work on that is somewhat easy to reason about.

Requirements are often hazy. Pushing back on that is good, but if the response is "do it anyway" then you either quit or handle the uncertainty as best you can. The latter makes estimating hard.

If you are going to have to depend on third parties (whether internal or external) that is another thing which can torpedo an estimate that was made in good faith. There would often be too much uncertainty in that situation to be able to accurately account for it in an estimate.

"estimates are always wrong" is obviously an exaggeration - the whole comment is written in that spirit.