The Torah gives specific commandments for farmers practicing agriculture in the land of Israel. God tells the farmer not to harvest the grain from the corners of his field. He tells the harvesters not to go over the crop a second time to capture produce they might have missed on the first pass. He tells husbandmen not to gather the fruit that falls from their vineyards and orchards on its own accord. Instead, they are to leave all of the secondary produce for the poor, the needy and the stranger to collect.
The businessman who conducts his operation in keeping with these biblical principles is not concerned only about his own personal success; he is concerned about the success of others as well.
It's not easy to leave the corner of a field unharvested, especially when you might be having trouble making ends meet yourself. How did the farmer find the resolve to follow this instruction? He had only to remember that the land did not really belong to him. He was only a sharecropper, so to speak, working the soil on God's land.
These laws provide the background for the story of Ruth, the great-grandmother of King David. Ruth was a destitute widow, living alone with her widowed mother-in-law, Naomi. When the wheat was ready for harvest around Bethlehem, Ruth went out with other poor women of the community to glean in the fields. She followed after the harvesters, picking up dropped sheaves and gathering the remnants that had been left behind. Gleaning is still permitted by law in modern Israel. Poor people are helped by it because they are permitted to pick as much fruit off the trees or from the ground as is needed when they walk through a field or an orchard.
These laws have application outside of agriculture. We all have fields that we work in. The idea is to leave a generous margin for the needs of others.
The sages point out that the Torah does not mandate how large the corners of the field have to be. A generous man might leave large corners standing for the gleaners while a stingy man might decide that a single stalk or two at the corner of each field is sufficient. In both cases, the man's field made a statement about his heart.