Cortes scuttled his ships to force his men inland

Cortes had sailed from Cuba in 1519 with roughly 500 men and eleven ships on an expedition the island's governor, Diego Velazquez, had tried to cancel and then tried to recall once it was underway. After landing near what became Veracruz, a faction loyal to Velazquez plotted to seize a ship and sail back to Cuba to report Cortes for insubordination, and rank-and-file soldiers, facing an unknown and vastly larger empire inland, wanted the same easy exit.

Punishing the plotters would not remove the underlying pull: as long as ships existed at anchor, some fraction of the expedition would keep calculating whether today was the day to cut losses and go home. Cortes needed his own force to face the interior with the same finality he wanted from them, not a promise they could quietly abandon under pressure.

He destroyed the ships, deleting the option to retreat so his men's only survival path was advancing inland.

A standing retreat option competes for attention and lowers the perceived cost of quitting at every hardship.

Destroying the ships collapsed the decision space to a single branch: survive by advancing.

Irreversible physical destruction is harder to plot against than a commander's authority.

To get full commitment, remove the fallback option yourself, visibly and irreversibly, rather than just persuading people to ignore it.

With no ships left, Cortes marched inland, allied with Aztec rivals such as Tlaxcala, and conquered the Aztec capital Tenochtitlan by 1521. The episode became the origin story for "burning your boats" as shorthand in English and Spanish alike for making a decision so total that retreat is no longer physically available.