Our life is like graphs of Trigonometric ratios. It may be up, down, plan, repeating, within certain limits but it's never constant. It's always changing. Certainly every one of us have experienced good and bad days.... i.e. having a positive or a negative value in different quadrants (stages of life) and it's different for different person like different ratios in different quadrants. And do you know what's the most interesting thing.... Adding a angle (theta) in different Trigonometric ratios can make them positive or negative. What according to you symbolize the theta in human life. It's the presence of a positive or a negative person under whose influence we shift to different quadrants. So it's very important to have a good theta in your life.