Lesson 05 · ChatGPT Mastery Pro ~10 min Instructions + Memory + pruning

Memory & instructions: teach ChatGPT to know you.

ChatGPT has two ways of remembering you: Custom Instructions, which you write, and Memory, which it learns on its own. Used well, they make it feel like it knows you. Used badly, they quietly make every answer worse. Here's what belongs where — and how to clean up Memory when it drifts.

The mental model

One is a contract. One is an observation log.

They both shape future responses, but they work differently and need different upkeep.

📝 Custom Instructions

You write them · permanent

What you explicitly tell ChatGPT about you and how to respond. Lives in Settings → Personalization, in two boxes.

The contract — always applied, never forgotten.

🧠 Memory

It learns automatically · has a soft limit

What ChatGPT picks up from your chats and stores on its own. Helpful, but it can save things that are wrong, stale, or that you never meant it to keep.

The observation log — useful, but needs auditing.

Do it · run the audit

Clean up what ChatGPT saved about you.

Here's your Memory panel. For context: you write in TypeScript these days, you run a weekly newsletter, and you often do want depth — not just quick answers. Review each item and decide: Keep the accurate, useful ones; Delete what's wrong, outdated, or sensitive.

🧠 Saved memories

0 / 6 reviewed

That's the audit. Notice the rule: you didn't delete things just for being personal — you kept the accurate, useful ones and removed what was wrong, outdated, or sensitive. Do this monthly and Memory stays an asset instead of quietly steering you wrong.

Quick check · what goes where

Instructions, Memory, or neither?

Three pieces of context. Put each in the right home.

Reference · the two boxes

Write Custom Instructions that work.

Settings → Personalization gives you two boxes — "what to know about you" and "how to respond." Fill both with process and style, never secrets.

TemplateBOX 1 — about you: Role: [your job] · Industry: [your field] · Main use: [what you do with ChatGPT] BOX 2 — how to respond: · Concise unless I ask for depth · Conversational, not stiff · use contractions · No "as an AI" disclaimers · When uncertain, say so · never invent statistics

Turn Memory off when…

Memory is on by default. Switch it off for:

Shared accounts (family/team) — memories get tangled.
Sensitive sessions — PHI, confidential financials, NDA-covered work.
Prompt tests where you want a clean baseline.

Turning Memory off doesn't disable Custom Instructions — the contract still applies.

Audit and rewrite tonight

Two tasks, 15 minutes. (1) Open Settings → Personalization → Memory and read everything stored about you — delete what's wrong, redundant, or shouldn't be there. (2) Rewrite your Custom Instructions with the two-box template above. Save, then test the difference on your next three prompts.

Try a prompt in the playground → Back to ChatGPT Mastery

What you can do now

Tell Custom Instructions (the contract) from Memory (the observation log)
Write Custom Instructions with the two-box template
Add to Memory deliberately with "Remember that…" — but keep critical context in Instructions
Audit Memory monthly: delete what's wrong, outdated, or sensitive; keep accurate-useful
Know when to turn Memory off entirely

Pro+

Up next in ChatGPT Mastery

Lesson 6 · GPT-5 agents: workflows that run themselves

Setting up agents to handle multi-step tasks — the use cases worth automating, the oversight patterns that prevent disasters, and the cost-control playbook. Start lesson 6 →