Six in the fourth place means

Contented limitation. Success.

Every limitation has its value, but a limitation that requires persistent effort entails a cost of too much energy. When, however, the limitation is a natural one (as for example, the limitation by which water flows only downhill), it necessarily leads to success, for then it means a saving of energy. The energy that otherwise would be consumed in a vain struggle with the object, is applied wholly to the benefit of the matter in hand, and success is assured.