そうりょうのじんろく

The younger child has more wit

総領=the eldest child, who is to inherit all総 the family's domain領 甚六=extremely甚 worthless六… 六(6), is pronounced ろく and is used in reference to 「ろくではない」, which means 'a good-for-nothing bum.' The idea is that the first born is pampered and sheltered, so they grow gullible and soft and ill-prepared for the real world