Whats is the khair 2

If the day and night of the person changes,  one will not be able to recognize the difference between khair (good) and Shar (evil).

If a person does a day _activity at night or vice_versa does a night activity in the morning he fails in distinguishing the difference between khair and Shar

How does the word khair (good) and Shar (evil) form?