Make a good use of the present.
An envious man grows lean at another's fatness.
Seize the day [Carpe diem]: trust not to the morrow.
He will be beloved when he is no more.
Had the crow only fed without cawing she would have had more to eat, and much less of strife and envy to contend with. [To noise abroad our success is to invite envy and competition.]
When you introduce a moral lesson, let it be brief.