I think in any real life scenario I would have an idea about the number of records in my table, or could figure that out very cost effectively. So to follow in OP's example with Rails, I would just do Table.where(id: [array_of_random_ids]), which is going to be extraordinarily more efficient than his batch processing Table.find_all.

Something should really only be filed under "Every Programmer Should Know" if it will be encountered in the real world more than once or twice. So in this case, the title feels like click-bait.