Why building a house almost always costs more than calculated

Correct, I hadn’t had that on my radar until 2 weeks ago either – but even today, I have no idea what it should cost.

To what extent does my question about supposedly easily overlooked (ancillary) costs "spoil" this beautiful thread?

No real costs are posted here, but the WHY is questioned.
Next door there is a construction cost thread with real numbers.

Does anyone have experience with what you should estimate for a curb lowering (6m for the driveway)?

I also think the question fits perfectly here.

For us, about €1800 for 6m length. However, it wasn't just the curb, but a sidewalk as well. So the curb was lowered and the sidewalk too.

I also think that the question fits perfectly here.

For us, about €1800 for 6m length. However, it was not just the curb, but a sidewalk as well. So the curb was lowered and the sidewalk too.

Thanks! Then I already have a rough direction. For us, it's only the curb itself, but a hydrant sign right in front of our driveway has to be relocated... I'm just estimating around 1,500.

There are said to be people who have relocated their hydrant sign on their own initiative and have adjusted the numbers on it accordingly so that the distances are correct. (the plastic clips with the numbers are available on Ebay...) I don't want to encourage anyone to do that, but as long as the numbers are correct and the fire brigade can clearly find the hydrant even in snow, no one really cares.

There are said to be people who have relocated their hydrant sign on their own initiative and adjusted the numbers on it accordingly so that the distances are correct.

After witnessing craftsmen install this blue sign at our place, I would say that such behavior is completely acceptable. I assume it marks the last shut-off valve. For me, a hydrant is something different (red and above ground).