This is the 12042nd most frequent Spanish word.
inflexible
Unwilling to change or adapt; rigid.
Here, 'inflexible' describes a person's strictness or rigidity in decision-making.
El jefe fue inflexible en su decisión de no aceptar cambios en el proyecto.
The boss was inflexible in his decision not to accept changes in the project.
In this sentence, 'inflexible' refers to the fixed nature of the train schedules that cannot be altered.
Los horarios del tren son inflexibles, por lo que siempre debes llegar a tiempo.
Train schedules are inflexible, so you must always arrive on time.
Here, 'inflexible' is used to describe the physical rigidity of a material that resists deformation.