What failed on Ferdinand de Lesseps´s plan was the choice to build the Panama Canal at sea level in order to evade the use of locks. The technical complications of working in the wet tropics doomed the project. Especially unfortunate were repeated landslides into the excavations from the near water saturated hills.
This mistake can be understood as De Lesseps was no engineer. His prior success on Suez Canal had laid solely in organizing the needed political and financial support and providing the technical support.