The concept is that an army who arrives by boat and burns them is committed to one of two things, winning or getting slaughtered. Its been adopted to mean that a team is committed to something ( retreat is no longer possible) irrespective of the consequences or outcome.
It mostly came from Cortes who burned his ships after landing in Mexico, so that his troops would be committed to destroying the Aztec Empire instead of turning back.
Note that the "turning back" would have happened not because the army wasn't committed, but because the Cuban Governor would have recalled Cortes. Spanish Colonial politics were delicate, I believe.