Certainly there's a lot to estimating in software dev, but I'm talking about when estimates are regularly wildly out of whack. Where someone or a team regular estimates something will take a few days but then it takes several weeks or months it indicates there's a problem or problems somewhere.
Maybe requirements are shifting too much. Maybe there's a lot of hideous technical debt. Maybe the wrong technology is being used to build the product. Maybe there are people on the team that don't have the skill level they need.
There could be a lot of things at play there, but the point is that there may be issues that need to be addressed. When you see wildly inaccurate estimates it means the root cause(s) should be investigated.
To a first approximation, everyone is bad at estimating software development times.
See: https://news.ycombinator.com/item?id=12149515 and https://news.ycombinator.com/item?id=4328660 and http://www.romenrg.com/blog/2015/09/28/why-asking-developers...
and The Mythical Man-Month, too.