AI Stack like a Human body

Sometimes the best way to make an AI agent is to just start creating it. But before you do, figure out which body part is actually missing.

Picture an AI system as a human body:

1. LLM is the brain. It understands, writes and reasons, but only knows what it learned in training
2. RAG is the brain with a library. It looks up your documents before it answers
3. MCP is the nervous system, a standard way to plug into your tools and data
4. Skills are muscle memory, saved know-how that loads only when a task needs it
5. An agent is the brain with hands to plan the steps and take the actions

A lot of teams jump straight to the hands. Gartner expects over 40% of agentic AI projects to be canceled by the end of 2027. Its recommendation: Use agents when decisions are needed, automation for routine workflows and assistants for simple retrieval. So before you add hands, name what's missing:

1. "It doesn't know our policies" = add a library
2. "It can't reach our CRM" = add a connector
3. "It does the task differently every time" = add a skill
4. "It has to make judgment calls across many steps" = now you need hands

Start with the brain and add extra parts only when needed.