In context, that expression refers to claims that contradict existing evidence.<p>For example, if someone finds a way to create mass&#x2F;energy, that would be extraordinary. All existing evidence suggests mass&#x2F;energy is conserved. Even if no one has tried XYZ before, the evidence of XYZ creating energy has to be weighed against the evidence of thousands of (other) processes <i>not</i> doing that. It&#x27;s possible someone made a mistake, or the results are being interpreted incorrectly.<p>While there is an ideal, the reality is that &quot;evidence&quot; is of varying types and qualities, and that perfect evidence is not always feasible.<p>In the US, criminal convictions (&quot;extraordinary&quot; claims) require proof beyond reasonable doubt. But civil convictions (&quot;ordinary&quot; claims) require only a preponderance of the evidence.