Christopher Columbus finds the New World
Christopher Columbus is largely credited with finding the "New World" of America, but he really landed in the south Bahamas. Wouldn't be too bad a miss, except for the fact that he was actually looking for a westward passage to the Orient.
You can't blame him for the blunder, this was long before our modern day luxuries of GPS, satellites or just good ol' paper charts.
While he might not have meant to find a New World, he certainly inspired others to follow in his footsteps and shaped the world as we know it today.
Despite two more voyages, Columbus died in 1506 having never found the elusive westward trade route he was after.