This chapter explores the ways in which Kirsti Teräsvuori (1899–1988) experienced and expressed loneliness on the pages of her diaries. The focus is on the diaries Teräsvuori wrote as a young woman in the early 20th century Finland. Altogether she wrote tens of thousands of pages of diary text in her life. Teräsvuori started to write her diary in 1916. At the time, she had to quit her studies and stay at home due to her illness. She did not fit in the norms of the society, and while she could not make herself visible in the everyday world, she made herself and her life meaningful by writing in her diary. Illness, isolation, and loneliness combine in her writings, and she wrote about those themes nearly every single day. There was a lot of suffering in Teräsvuori’s life and her writings. But in the end, it was also her loneliness that made it possible to start to write a diary. Or actually, loneliness was what she needed to be able to write, and loneliness was also productive. Overall, writing was an essential act, and Teräsvuori wrote a diary collection, which is very special in many angles.