Imagine you are an employee of a company which has the office in a high office building. Every day you had chosen the stairs instead of the elevator in order to keep yourself fit in this way. One day you were in late because you overslept. You decided to save a couple of minutes and use the lift. You got inside and started your journey upward. Suddenly it halted and the ligths turned off. You wanted to push the emergency button but it didn't operated.
