In the early twelfth century an Italian architect made a mistake. He built a tower on a piece of unstable soil. It was probably not totally his fault – those commissioning the bell tower wanted it to be close to the cathedral, and building methods back then were not quite what they are now. Still, historical record leaves us unsure exactly who was responsible for the mistake, which saw the bell tower of Pisa begin to lean only a few years after its lower levels were built.
no one deemed it necessary to pull it down and start again somewhere
more stable, they just left it for a while and went off to war, leaving
the remainder of the building project to become someone else's' problem
years later. Sure enough, peace reigned again and about a century later a
confident set of builders added a few extra bricks on the subsiding
side to straighten the tower as it grew upwards. Not entirely
successfully but it didn’t fall over which was a good result.