How should I know if my hair is healthy or in a bad situation?

Such a question usually occurs into my mind and I found some hens show that; if we need to know whether our hair live in a good condition or bad, we should test strands from four different areas in our head while the hair is wet… then hold these strands and stretch them… if the hair stretches and turns to its original length when released, then the hair is in a good condition… however, if the condition happens to be otherwise, we should then hurry up to start taking an immediate care of our hair…