This idea is concretely explained by Dr. Sriram a renowned spiritual scientist. He explains this as part of our experience as dualistic.. do visit his web sites Eye on I, Journey unto Joy and Roots of Happiness series..
A pertinent question baffling best brains of humanity and students of positive psychology.. i am repeating my beloved SIR's words.. HE says... '"one can notice the change in one's mind and body, when we are about to be taken over by negative emotions. educating one's emotions is the key. just as you clean your physical body you have to clean your mind and heart every day.. and this is what real meditation or yoga is all about. you meditate on human heart, on the negative emotions that it contains and you remind yourself every morning that you have this capacity to clean, and, clean the 'psychological dust' that has settled on you heart and, be aware and be aware to clean them and keep them under a healthy control.."'