Once the Bodhisatta was born as a rich merchant in Benares.
One day his son, sitting on his lap, asked him for one word which comprehended all things. The Bodhisatta said it was "skill" (dakkhayya).
The story was told in reference to a lad in Sāvatthi who asked his father "the Dvārapañha" (question regarding the entrance to the Path). The father, not being able to answer the boy, brought him to the Buddha. J.ii.236f.