Thy gift, thy tables, are within my brain
Full character'd with lasting memory,
Which shall above that idle rank remain
Beyond all date, even to eternity;
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He has committed a serious fault in carelessly giving away a gift which he appears not to have used. Yet this was from the beloved whom he claimed to love more than anything else in the world. He can only excuse this fault by claimimg that all is retained forever in the security of his mind, or, if not forever, for as long as he lives and breathes. This is something of a descent from the heights of immortality. But what else can be done - the fault has been found out and an excuse must be invented? In the circumstances this is not a bad one, and the youth has the additional satisfaction of being told that he will always be at the forefront of his lover's thoughts.
It is possible that the poem is the result of a gradual cooling off over a longish period. The youth was away, (perhaps imprisoned in the Tower) and the lack of contact led to forgetfulness, a disregard of the past and the discarding of the notebook. On his unexpected return the youth enquired after it, and had to be met with evasions and excuse. It seems unlikely that the notebook is the one referred to in sonnet 77, now filled with the youth's own memoranda. For the giving away of such a treasure would be an unforgivable act, rather like the loss of Desdemona's handkerchief. shakespeares-sonnets.com
The poet admits to having given away, or to having lost, a notebook which was a gift to him from the youth. The insignificance of the event has led commentators to believe that the detail must be biographical, for it is too trivial to be part of a traditional sonnet sequence of lofty sentiments, and therefore probably relates to an actual incident. The idea of tables (a notebook) to record the loved one's perfections had already been used by Ronsard in one of his sonnets. The difference seems to be that Ronsard's sonnet expresses the ideal of a sublime love, whereas Shakespeare seems to relate much more to the untidiness of lived experience.