&gt; The Challenger failed because, while the O-Rings were within tolerances, they shouldn&#x27;t have been varying at all. So because they were varying unexpectedly, they inevitably failed.<p>That&#x27;s not entirely correct.  The idea that &quot;the o-rings were within tolerance&quot; isn&#x27;t right.  There is effectively no tolerance on the o-ring, either it&#x27;s very, very nearly perfect or there&#x27;s something wrong with your design, just like the bridge.  The o-rings should be getting immeasurably small amounts of wear so the idea that they were &quot;only&quot; burning up 1&#x2F;3 is a <i>huge</i> red flag.  Any measurable wear on them is a problem, so 1&#x2F;3 of them being gone means they were perhaps 30 or 300 times over tolerance.