Only after a cow dies do people realize how much milk it gave them.
What it means
While the cow lives, its milk is taken for granted; its worth is seen only once it is gone. The proverb speaks of people recognizing, too late, how much someone gave to their lives.
Source: Gikuyu (Kenya) oral-tradition proverb — "African Proverb of the Month," January 2022 (afriprov.tangaza.ac.ke)
The source explains it: often used at funerals when relatives and friends realize how much the deceased person contributed to their lives. The wording of the meaning is ours.