---
title: "ChatGPT Custom Instructions Not Working? Here's Why"  
description: "ChatGPT Custom Instructions Not Working? Here's Why"  
author: "Yogendra  Mohan"  
published: 2026-09-02  
updated: 2026-09-02  
canonical: https://answers.mindstick.com/qa/117141/chatgpt-custom-instructions-not-working-here-s-why  
category: "GPT"  
tags: ["gpt", "chatgpt"]  
reading_time: 1 minute  

---

# ChatGPT Custom Instructions Not Working? Here's Why

**I told ChatGPT to always write in British English and keep paragraphs short. 30 messages later it's back to American spelling. Why did this happen?**

## Answers

### Answer by Manish Sharma

It's not ignoring your prompt; it literally can't see your first message anymore. Every chat has a limit on how much it can hold, and once you cross that, the old stuff drops off the top. There's no warning; it just quietly happens.

Two ways around it. The lazy way is to repeat your rules every 10 or 15 messages. The proper way is to put them in Custom Instructions (Settings, then Personalisation) so they apply to every chat without you having to type anything. If it's for one piece of work, make a Project and stick the rules in there.

And honestly, when a chat gets that long, it's time to start a new one anyway. Copy the useful bits, paste them into a fresh chat with your rules on top. Works better than fighting with a bloated thread.


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Original Source: https://answers.mindstick.com/qa/117141/chatgpt-custom-instructions-not-working-here-s-why

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