The first European to discover New Zealand thought he was in South America!
Everyone makes mistakes, but they tend to be a little more drastic when you're a renowned seafarer and explorer.
Abel Tasman was a Dutchman best known for his merchant voyages of 1642 and 1644 with the United East India Company and is the first known European to reach what is known today as Tasmania and New Zealand.
Of course, he thought he was on the other side of the world.
Tasman intended to sail north but the wind didn't cooperate so he ended up steering east. On December 13 he sighted land and named it Staten Landt, assuming that it was connected to Staten Island, Argentina off the southern tip of South America. From there he sailed north and then east, finally anchoring five days later 7 km from shore.
After trying to land and gather water he was attacked by the Maori, losing men in the process. The area was known as Murderers' Bay. Of course, in modern times, that name would not fly—so you can now find it as Golden Bay on a map.