In contrast to the Soft Deadline a “Hard Deadline” is a deadline that you MUST meet, otherwise the results are catastrophic,
Some easy examples are activating the brakes on a car, if there is too much of a delay on hitting the brakes, the car may be liable to hit a wall
Another example is that of a airbag deploying:

Further Examples:
Sensory data acquisition; • data filtering and prediction; • detection of critical conditions; • data fusion and image processing; • actuator serving; • low-level control of critical system components; and • action planning for systems that tightly interact with the environment.