what does this mean?

<p>I am reading a medical science book right now...and there's an allusion to one of Dr. Parkes Weber's quotes: "For one common disease or syndrome there are several rare ones"...and then it says, "In other words, each rare condition is by itself rare but when all the rare conditions are added together, it is not really that unusual to come across something strange"...</p>

<p>Now i cursorily understand this quote but i am having a hard time breaking down its semantics....I really don't know what this is saying....how can an aggregate of rare conditions be perceived as a common phenomenon?</p>

<p>Any one may be rare by itself, but there are so many rare conditions out there you are likely to see one of them.</p>

<p>oh wow.....ok thanks alot! i thought there was a deeper meaning...</p>

<p>My guess would be the "deeper meaning" is that one can't ignore learning about/being aware of rare conditions since, as stated above, the odds that you'll see at least one of the rare conditions are high.</p>

<p>Over the course of your career as a physician the diseases you see are overwhelmingly going to be common ones but the aggregate number of rare diseases is so great that even though the chances of seeing one in any particular patient are small, if you see enough patients you will almost certainly encounter a rare disease eventually.</p>