An old Jewish parable, adapted somewhat to new ends:
A man planted a vineyard, hoping to grow grapes. But the grapes were wild and useless. Because his planting did not succeed, he tore it up and, sorting out the good grapes from the bad, planted again. Again it did not succeed, and again he tore it up and, sorting out good from bad, planted again. This third time did not succeed, either, and so he tore it out, cleaned it, and planted again. And how long did the man keep this up? Even until the thousandth generation.