Thermodynamics.

Every day I can feel entropy tugging behind my skin, separating the outermost cells and sacrificing them to the universe in contribution to my continual offering, the tribute that keeps me alive. The environment harvests heat from my chemical reactions, and in return, I keep my consciousness, my ability to speak and think and act. I give more to the universe than I take and organize within my body, so it lets me live. And the moment those weighted scales fall out of balance--when for once I sequester more than I produce--the indomitable force will eat me alive. I will decay; pieces of me will disseminate to feed its insatiable lust for disorder. This is death; entropy dissolves anyone who can't pay tribute. As long as it destroys more than you create, it's satisfied, but don't try and come off conqueror, because there's more of it than there is of you.

And ΔS(universe) must always be positive.
Always.