Homeostasis refers to the ability of your body to maintain an internal balance while adjusting to external factors. Put another way, homeostasis ensures that whatever extreme situation occurs around you, say a blizzard or sweltering heat, your body will keep itself in check so that you won't come into harm's way. Homeostasis is not always in the context of body temperature but we will use that as an example to illustrate its importance.
When Body Temperature Goes Wrong
As warm-blooded animals, the human body can amazingly keep us at the correct temperature despite our surroundings. For example, we shiver when we are cold to produce heat. Something that simple can actually save your life! However, in certain situations, the body may fail to shield us from Mother Nature and homeostasis doesn't work. At this point, sitting outside in the cold will start to affect you very badly.
It's a Cold World
If you are in the cold for too long, even shivering might not help and homeostasis may not work. Hypothermia is when your body temperature drops below the normal standard needed for your body to function correctly. Think about the coldest place you've even been. Now think about being there for about an hour longer than you were then. After awhile you probably couldn't even move, right? The same thing happens inside your body. If your temperature is too low, normal events can't work, including homeostasis. When your body is put in an extreme situation for too long it can shut down, leaving you defenceless to many things such as hypothermia.