First you plant the four inch seedling then work to keep the deer from nibbling their tender shoots. As the years pass you begin the thinning and limbing process. You guard your young forest against disease and fire. Retirement age comes and you haven't cut or sold any logs. You've seen no payback for your years of sweat and toil.
Many foresters die without seeing the harvest.
In Sunday School you teach children who know how to get under your skin. But you keep on taking it. You do it because you have the long view. In 50 years you see that unruly child becoming an oak of righteousness. You keep teaching because you are a servant of the Living Lord.