Stamina It's the energy of the character. It falls as time goes by. Winter makes stamina to drop faster, as well as age. You recover your stamina by eating, it sounds easy.
Stamina max The age of the character determine maximum value for stamina. Younger and elder characters have lower max than medium-aged ones.
Knowledge Older characters know more about life, and are able to surpass the drop of his stamina max fall.
Water You need water for life. Don't forget. When you are very thirsty you are a worse hunter.
Poison People and some plants put poison in your very life. Be careful because you can not remove it from your body, and it will make your stamina falls.
Pollution Pollution came from some human activities. As you live next to this activities your body become polluted. You can clean yourself by living away from this pollution sources.