When you reach the dead-ends of happiness or anything that is happiness-related, you feel like you want more and more.
Because happiness is overrated, you feel unsatisfied. But your human body is either incapable of more or cannot handle more. Only then you become blue. You become blinded by blackness and life meaninglessness.
I, like Hamm, cannot stand.
I, like Clov, cannot sit.
Your life simply becomes an abiding manifestation of an endgame.