Choosing hydrogen as the gas to inflate an airship. Introducing rabbits to Australia. They had no natural predator on the continent and rabbits breed like…well, you know.  Rejecting the first Harry Potter book. You have to wonder if those 12 publishing firms have gotten over it yet. You also have to wonder if the acquisitions editor responsible at all the firms is still employed.  Ireland. After conquering England, a Norman stood on a west coast cliff, saw a distant shadow of land and thought, "Close enough. Let's have it too."  Deciding the aesthetics of uninterrupted deck space was of greater importance to its first class passengers than the number of lifeboats on the Titanic. Invading Russia. For some reason, armies tend to forget that it's a big country and winter is coming. Russian winter. Vietnam. Enough said, really. Deciding to follow George Donner and James Reed and abandon a well-known wagon train route known as the California Trail in favour of a...