Chunks too large and retrieval loses precision; too small and you lose context. Chunking is the most underrated part of RAG — pick the wrong strategy and no amount of downstream optimization will save you.
When you split a document into chunks, each chunk loses its place in the original document. Contextual Retrieval solves the isolated-chunk problem by injecting a document-level summary into every chunk at index time.
A RAG system needs data to answer questions, but data only accumulates as the system gets used. Cold-start strategy is what bridges the gap from empty to useful.