What always make me so sad on reading this and the...

What always make me so sad on reading this and the other sonnets (such as "Shall I compare thee") addressed to "the master-mistress of my passion" is that, since we don't know who he was (despite the dedication, and despite the assertions of writers such as A. L. Rowse), the promise of eternal life due to the poetry is made pointless by the anonymity of the individual. R