[true_religion]

Estimates can be fairly accurate if they're made for software that's a composition of previously iterated work.

If someone asks for a login system with X,Y,Z and you've done that 1000 times, you can be fairly accurate in stating what it will take to do it 1001 times.

The issue is when a piece of software is custom, and there's no domain expertise available for the custom bit then you cannot accurate estimate how long it will take because the developers will be learning while doing.

[ams6110]

And some developers bring this on themselves. They could use the boring conservative technology that they know inside and out from the last project, or they could use something that's new and hot this month, which they have never done or have much less experience with (but is exciting).

Double whammy if it's an unfamiliar domain and a cutting-edge tech stack.

[Scarblac]

And it takes longer, so more billable hours.