I see two ways of looking at this. One is that a Google search turned up only one reference to the Vineyard Principle, and it was in business marketing. It is, as Juliet Christie says, about nourishing all the grapes on the vine, not only the ones that ripen first. The idea in marketing is to build relationships with customers who don't buy immediately. The grape is the customer, and you want to nourish them until they are ripe to buy.
But the metaphor of the vineyard goes much deeper than that, back to the Bible, and it is connected to developing human goodness and leaving cruelty behind. It is "As you sow, so shall you reap." This teaches the lessons of the farmer (or grape-grower) with regard to all of life. We must plant good seeds. We must be patient. We must weed daily, water well, and keep pests away. And, once the harvest begins, we must wait for ripeness, but then pick quickly, before the fruit rots on the vine, and before it is eaten by animals or bugs. Lots of attentive care of our good crop is essential to produce goodness - in ourselves, in our children, and in all life around us.
Focusing on the vineyard, in particular, one might add two things. A grape vine can be cut all the way back to a bare stem, and still regrow. Just so, a person who loses everything, like Job, can return to prosperity if he remains faithful. And, at the end of the process, at the time of harvest, especial care must be taken. The vine is full of riches that many will want to steal, and also will rot quickly.
Let us learn to nourish goodness all the way through life, to be patient, and to take especial care in the harvest.
Only then will human cruelty and indifference pass away. And then "each man shall live beneath his vine and fig tree, alone and unafraid" as the old song, based on Isaiah, says.
My hubs on Stephen Covey's 7 Habits of Highly Effective People, and my hubs on Zen all talk about this. In the East, it is called the Law of Karma.