Language represents a way for us to communicate abstract ideas and concepts. It has evolved as a human-only form of interaction for the best part of the past 100 million years. Translating that into something a machine can understand is (unsurprisingly) difficult.
Modern(ish) computers appeared during and around WW2. The first application of natural language processing (NLP) came soon after with the Georgetown machine translation (MT) experiment in 1954. In the first decade of research, many expected MT to be solvable within a few short years  — they were slightly too optimistic.
This is a companion discussion topic for the original entry at https://www.pinecone.io/learn/unsupervised-training-sentence-transformers/