Mother Monkey had two babies. One was reared with love and one with neglect. The loved one was smothered and died; the other grew despite neglect.
The best intentions will not always ensure success.
[Note: Also see The Ape and her Two Young Ones.]

Townsend version
The monkey, it is said, has two young ones at each birth. The Mother fondles one and nurtures it with the greatest affection and care, but hates and neglects the other. It happened once that the young one which was caressed and loved was smothered by the too great affection of the Mother, while the despised one was nurtured and reared in spite of the neglect to which it was exposed.
Moral
The best intentions will not always ensure success.

Babrius Translation (The Monkeys)
Twins at each birth the female monkey bears,
Yet gives not them her love in equal shares.
For, by her illstarr’d fondness one opprest
Is kill’d with kindness in her rugged breast.
The other as a useless idiot thrown
Adrift, an outcast, thrives when left alone.
Men’s natures oft are such, that friendliness
In them than hate is to be chosen less.

Simia et Gemelli Eius
Simia, ut ferunt, cum peperit gemellos, alterum diligit, alterum negligit. Erat puerpera cum gemellis atque, cum incidisset terror, vitatura periculum, dilectum prehendit ulnis. Quem, dum praeceps fugitat, collidit petrae atque enecat. Neglectus autem, qui in hirsuto haeserat tergo fugientis, mansit incolumis.
Perry #218