At the end of The Three Sisters, Olga, Masha, and Irina have just survived the death of a fiancé, the abandonment of a lover, and eviction from their own house at the hands of their sister-in-law. Chekhov writes in the stage directions, "the three sisters stand close to one another" (4.174). They may have lost pretty much everything else, but they have each other.
In that support, the women seem to find some resilience—even hope. Olga feels better when she imagines that "our sufferings will turn to joy for the people who live after us, their lives will be happy and peaceful, and they'll remember us kindly and bless us. My dears, my dear sisters, life isn't over yet… the music sounds so happy, so joyful, it almost seems as if a minute more, and we'd know why we live, why we suffer. If only we knew" (4.177). Inspiring, huh?
This search for meaning, this not-giving-up, is contrasted with Chebutykin's nihilistic "What difference does it make?" (4.178). (For some textbook nihilists, refresh your memory of The Big Lebowski. You know: "We belief in nosing.") Anyway, back to Russia. The doctor is totally disengaged from life, while the sisters keep trying to understand and improve it.