Litost is what you feel when you realize just how shitty your life is. It's that strange mixture of despair and desperation, of frustration and futility that comes with realizing how unsuccessful you've been in the endeavors you've undertaken recently.
Sometimes, you feel it at the end of a shitty day at work. Other, less fortunate people, feel it every night when they go to bed. It's a tough reality, and Milan Kundera was right to define it as "torment".