Happiness is a matter of perspective; its a state of mind. Happiness is not a real thing beyond a state of mind. You can never find happiness, nor can it enter your life; it is how you define the state you are in.
That idea of becoming like water is a good analogy. You can only be or not be, though how you feel about the situation can be a distraction to how you will persist within the situation.
I do wonder how many other animals/beings rely so much on their mental/emotional state to fuel their actions. Do they even have these states to enter at all?