What are the main limitations of a basic RAG system?

Basic RAG suffers from poor retrieval on complex queries, loss of context across chunks, irrelevant top-k results, and inability to handle multi-hop questions that require combining information from many sources. It also struggles with structured queries like aggregations, with queries that need world knowledge plus retrieved facts, and with documents whose meaning depends on surrounding context lost during chunking. Adding query expansion, reranking, hybrid search, and graph-based retrieval addresses most of these failure modes in production.