Martin Frobisher: Attempting to discover the coveted Northwest Passage, Frobisher lost two of his three ships in a storm and five men to kidnapping by the native Inuit – but discovered a black rock on Baffin Island that he was convinced, despite its color, was gold ore. Organizing a second, larger expedition and braving an ocean crossing with dangerously overloaded ships, he brought back 200 tons of the rock...which turned out to be a very large amount of iron pyrite. Undeterred, Frobisher rallied a third, even larger expedition of 15 ships and brought home another 1,300 tons of gold ore...which again turned out to be iron pyrite.
Robert Falcon Scott: Despite a head start over Amundsen and superior resources, Scott's British expedition to the South Pole quickly went nowhere. Scott ruled out skis as too cumbersome and dangerous, didn't bring enough food for his men, decided to use ponies instead of sled dogs (they inconveniently sank belly-deep in the snow and froze to death, while Scott insisted his men desperately try to keep them alive), and tragically set his final supply depot 35 miles north of the spot he had planned for it. After reaching the pole only to find Amundsen had already come and gone, Scott and his men died on the return trip, 11 miles shy of that final depot.