The belief in a built-in unfairness in life energies (Marx focused on the inequities, struggling for justice; his orientation not particularly self-actualizing re labor).
A personal obscurantism that frustrates (Schopenhauer had this: a rather inordinate will-sensing, taking the side of his depressive father, therewith combined with an ongoing, gloomy abreaction re his mother's bonhomie ---> to inability to perceive Will as Good).
Soren Kierkegaard's father Michael had "cursed God" re his poverty, and the melancholy father thus influenced Soren's rather dour aspects. In a sense, the later wealth which Michael bequeathed to Soren permitted a Platonic-type of leisure enabling Soren to contemplate upon life.
Jean-Paul Sartre lost his father at 2, and was subsequently heavily bullied as a child and teenager.
Albert Camus lost his father, never met him, grew up in poverty, and was influenced by Nietzsche (who'd lost both his father and his brother, both unexpected, but the latter death vividly seen in a precognitive dream by Friedrich) and Schopenhauer. Camus began with Plotinus, a philosopher of great insight, profound depth, and hope, but Camus primarily worked out his perspective as a pessimist, until the close of his life, when he picked up the grace of Christianity, influenced of and inspired by early Christians he'd studied along with Plotinus.