Incentive

"Nansen had moreover introduced a startling new concept into Polar exploration. He had deliberately cut off his lines of retreat. His route was from the desolate east coast to the inhabited west. This was not bravado, but calculated exploitation of the instinct of self-preservation. It drove him on; there was no incentive to look back."

-Roland Huntford, 

"The Last Place on Earth: Scott and Amundsen's Race to the South Pole"