Clearly, their are outside events that could bump us to one of those extremes. In life, great things happen; terrible things happen. When they do, we honor whatever feelings come up at the time, and we take appropriate action.
Santosha is more a state you want to maintain in daily life. It keeps you off the emotional roller coaster of dramatic extremes that can drain your energy. It puts you in a state of equilibrium that allows for steady energy, clear thinking, access to your intuition, and greater authenticity. Cultivating a sense of contentment with what you have and who you are has great side effects, too: it reduces the need for retail therapy, shopping and accumulating as a soothing measure.
For more on how you can develop Santosha, contentment, see Day 15 of Yoga Mind: Journey Beyond the Physical.