How do I prevent ChatGPT from making up incorrect information?

ChatGPT has a tendency called 'hallucination' where it may make up answers and speak with certainty even when it doesn't actually know something. To prevent this, include a prompt like 'from now on, if you do not know the answer to a question, just tell me you don't know. Do not make up an answer.' ChatGPT will acknowledge this instruction and will then inform you when it's uncertain rather than fabricating information. Always apply your own filter as responses are typically 80-90% good but require verification.