General contractors — the ones whose names you see on hoardings at the biggest building sites — aren’t exactly builders. General contractors don’t dig holes, pour concrete or fix pipes. General contractors are in the business of managing risk.  Building sites are uncertain and complex. A million things can go wrong. The general contractor’s job is to accurately forecast what will go wrong, and how much it will cost to fix it, for years into the future. If they bet correctly, and manage the job well, they get to make a small profit.  Anyone who’s extended their kitchen knows construction…