[jonaf]

I purchased new construction once. They were putting up a thousand cookie cutter houses like ours in that neighborhood. And even that estimate missed the mark by more than 3 months. Even estimating building the same floor plan the hundredth time is hard!

Now imagine, you are tasked with building a house with no floor plan. You have to procure some materials last minute, and at least two of the materials you must create from raw materials. Occasionally, you have to remove structural parts of the house to account for changes to the requirements. Someone built their own power tool instead of using the out of the box nail gun, which injured a fellow worker and required replacement of drywall. The crew had a holiday, then it rained, then a shipment of materials was delayed. After your electrician recovered from the stomach flu, he was unable to wire the house for ceiling fans -- a late stage increase in scope from the customer -- because one of the workers wanted to learn a new technique for framing for the block and wire, which he read about on hacker news. When the construction is 95% complete, the boss asks the crew to go ahead and start on another build. Another month elapses, and the home is nearly done. Your office contacts the customer to schedule closing, only to discover that the customer changed their mind and got an apartment 6 months ago. All is not lost, however: your boss receives a bonus for a job well done, which he thanks you for. Good job! A few months later the home is found to be in violation of a recently ratified law making smart homes illegal in the county, but no one involved in its construction works there anymore so they'll each likely repeat the mistake at least once more.