Rav Chiya bar Adda was tutor to the children of Resh Lakish. One week he vanished for three days without explanation. When he returned, his employer, one of the sharpest minds in the academy, wanted to know where he had been.
I have a vine, said Rav Chiya. My father left it to me, trained up on high trellis-work as a great bower. On the first day I went to pick it, I gathered three hundred clusters, and each cluster gave a gerav of wine. That is no small thing. A gerav holds about what two hundred and eighty-eight eggshells could hold. Three hundred geravs of wine in a single morning. It was the richest harvest of my life.
On the second day, he continued, I gathered another three hundred clusters. But the grapes had shrunk. It took two clusters to make a gerav. On the third day the same three hundred clusters yielded only one gerav for every three bunches. By then the season was fading. I left more than half the grapes on the vine for anyone who wanted to come gather them. That is why I was gone.
Resh Lakish listened to the whole accounting and then delivered his verdict. If you had not been so negligent, he said, if you had not skipped three days of teaching my children and rushed back to me instead of to your vineyard, the vine would have yielded more.
This exchange from tractate Ketubot 111b, preserved in Hebraic Literature (1901), carries the classic Resh Lakish sting. A teacher's first field is his students. When he neglects that field, heaven quietly stops watering the other ones.