I think part of the miscommunication may lie in professional idiom. In medicine, all diagnosis is provisional and statistical - which both elevates &quot;probably&quot; to &quot;certainly&quot; in casual conversation, and renders most absolute statements hollow. It&#x27;s just an automatic translation that has to happen: when you tell someone with a three-day sniffle that they have a cold, it&#x27;s an absolute statement aloud, but in your head you have to honestly say &quot;99.999% cold; 0.0009% HIV; 0.0001% cancer.&quot; And you have to treat them accordingly, until proven otherwise, because if you try to rule out cancer on everyone with a sniffle you&#x27;re going to actually kill more people with complications than you&#x27;ll ever save.<p>&quot;This person has X&quot; most of the time means &quot;X has a strong statistical advantage in explaining this patient&#x27;s symptoms, so we&#x27;re going to pursue treatment for X until accruing evidence suggests we shouldn&#x27;t.&quot; I guess that&#x27;s not always true, given a few things that exist by definition, but it&#x27;s mostly true.<p>And that&#x27;s generally good enough, since... well, statistical masses tend to obey statistical properties.