---
title: How Reasoning Fails
seo_title: How Reasoning Fails — video
description: 'Sycophancy, shortcut learning, specification gaming and cascading failures: the failure modes of reasoning models, how to detect them and how to mitigate them.'
keywords: reasoning model failures, AI sycophancy, shortcut learning, specification gaming, LLM hallucinations, reasoning chain, systematic LLM errors, CoT unfaithfulness
date: '2026-04-09T00:00:00+00:00'
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    <h1>How Reasoning Fails</h1><p>Sycophancy, shortcut learning, specification gaming and cascading failures: the failure modes of reasoning models, how to detect them and how to mitigate them.</p>
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    <div class="s5-video-watch__section-head"><span class="s5-eyebrow">Video summary</span><h2 id="video-summary-title">The ideas to retain</h2></div>
    <div class="s5-video-watch__snippet-grid"><article><span>01</span><h2>1. Failure types</h2></article>
<article><span>02</span><h2>1.1 Shortcuts — shortcut learning</h2><p>The model learns to solve a problem using superficial correlations instead of the underlying reasoning. The result is correct on training and evaluation data where those correlations hold,…</p></article>
<article><span>03</span><h2>1.2 Systematic errors</h2><p>Models have systematic biases that produce non-random errors on particular categories of input. Some of the best documented are:</p></article></div>
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  <aside class="s5-video-watch__source"><div><span class="s5-eyebrow">Context and evidence</span><h2>Continue with the full article</h2><p>The chapter develops the mechanism, primary sources, limitations and connections to the rest of the series.</p></div><a class="s5-video-watch__source-link" href="https://5sigmas.com/en/series/modelos-razonadores/02-fallos/">Read the article →</a></aside>
  <section class="s5-video-watch__related" aria-labelledby="related-videos-title"><div class="s5-video-watch__section-head"><span class="s5-eyebrow">Next step</span><h2 id="related-videos-title">Related videos</h2></div><div class="s5-video-watch__related-grid"><article><a href="https://5sigmas.com/en/videos/series/modelos-razonadores/05-riesgos/"><img src="https://5sigmas.com/en/series/modelos-razonadores/05-riesgos.jpg" alt="" loading="lazy" width="1280" height="720"><span>Reasoning · 1:00</span><strong>Reasoning Risks and Production Controls</strong></a></article>
<article><a href="https://5sigmas.com/en/videos/series/modelos-razonadores/04-latencia-streaming/"><img src="https://5sigmas.com/en/series/modelos-razonadores/04-latencia-streaming.jpg" alt="" loading="lazy" width="1280" height="720"><span>Reasoning · 0:59</span><strong>Latency, Streaming and Product Design</strong></a></article>
<article><a href="https://5sigmas.com/en/videos/series/modelos-razonadores/03-test-time-compute/"><img src="https://5sigmas.com/en/series/modelos-razonadores/03-test-time-compute.jpg" alt="" loading="lazy" width="1280" height="720"><span>Reasoning · 1:00</span><strong>Test-Time Compute</strong></a></article></div></section>
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