Why AI gets things wrong: understanding hallucinations

Why AI states wrong things with confidence, where it slips most often, and how to check its answers.

Key ideas

1. 1

   It continues text plausibly

   Given a question, an LLM doesn't search for facts; it continues the text with whatever is likely to come next. Usually that prediction is right, but even when it doesn't know, it keeps going and produces something that sounds right.

   Stating something untrue with confidence like this is called a hallucination. The real problem is that the tone alone won't tell you a right answer from a wrong one.

2. 2

   Where it slips most

   Mistakes follow patterns. If an answer contains any of the five below, check those parts first.

   Some assistants search the web as they answer, but they can still misread what they find or lean on the wrong page, so the same checks apply.

   Five common trouble spots, and how to check them

   Where	How it goes wrong	How to check
   Numbers and dates	Statistics, years or amounts slightly off	Compare each figure with the original source
   Quotes and sources	Papers, articles or links that don't exist	Open the link and check the title and content
   Recent events	Doesn't know what changed after its training data	Look for a dated official announcement
   Names	Mixes up similar people, companies or products	Check the official site or the original text
   Long calculations	Slips in a middle step	Redo it with a calculator or a spreadsheet

3. 3

   Ask in ways that reduce mistakes

   Paste in the material and ask it to answer only from that, and there's less room to invent. Tell it that "I don't know" is an acceptable answer, and ask it to quote the sentences each answer rests on.

   With the quotes in hand, you can check just those sentences instead of rereading the whole source. Ask for sources without supplying any material and it may invent convincing quotes and citations — so always give it the material.

   None of this removes mistakes entirely, so the checking habit in the next step still applies.

   Answer the questions using only the press release below. If something isn't in it, say "Not in the source," and quote the sentence each answer comes from.
   Questions: When does it launch, and what does it cost?
   [Paste the press release]

   Launch date: 13 October — source: "It is available worldwide from 13 October."

   Price: Not in the source — the press release doesn't mention a price.

   Check it

   • Search the source for each quoted sentence. If a quote isn't actually there, discard that answer.
4. 4

   Make checking a habit

   You don't need to doubt every answer. But numbers, names, quotes and links that go into anything you share must be checked yourself.

   Check it

   • Mark every number, name, quote and link in the answer.
   • Check each one against the original source or the official site.
   • For anything a decision depends on, confirm it with a second, independent source.