De Lesseps's Suez triumph made him overconfident about Panama

Ferdinand de Lesseps had successfully built the Suez Canal through flat Egyptian desert, and McCullough shows how that success created a dangerous overconfidence when he turned to Panama — a wildly different environment of dense jungle, mountainous terrain, torrential rain, and disease-ridden swamp. De Lesseps assumed that willpower, financing, and the same sea-level design that worked in Egypt could simply be transplanted to Central America.

This assumption proved catastrophic. Panama's terrain required cutting through mountains, not flat desert, and its climate bred disease at a scale nothing in the Suez project had prepared French planners for. De Lesseps largely dismissed warnings from engineers and doctors who understood the specific challenges of the isthmus, treating skepticism as defeatism rather than useful information.

McCullough uses this as a broader lesson about the danger of pattern-matching a previous success onto a genuinely different problem without examining whether the underlying conditions actually transfer.

Takeaway: past success in one context is not proof a strategy will transfer to a different one — check whether the underlying conditions actually match.