And then without observing that he was departing from the true line of his talk, he was more than likely to hurl in a long-drawn parenthetical biography of the writer of that letter; and you were lucky indeed if he did not take up that writer's relatives, one by one, and give you their biographies, too.
Such a memory as that is a great misfortune.

To it, all occurrences are of the same size.

Its possessor cannot distinguish an interesting circumstance from an uninteresting one.

As a talker, he is bound to clog his narrative with tiresome details and make himself an insufferable bore.

Moreover, he cannot stick to his subject.