In the first episode of The House of Cards on Netflix, in its first scene, Kevin Spacey acting as Frank Underwood, comes out of his home in the dark, late in the evening, after hearing a dog crying hit by a car which drove away without stopping. The dog was in intense pain and it looks like it is going to die after hours of battle with pain. He decides to kill the dog to end its pain.
And he says there are two kinds of pain in the world. One is useful pain which makes us stronger. The other one is the useless pain which must end.
The biggest problem is we do not know which pain is useful and which one is useless.