Six at the beginning means:

Seeking duration too hastily brings misfortune persistently.
Nothing that would further.

Whatever endures can be created only gradually by long-continued work and careful reflection. In the same sense Lao-tse says: "If we wish to compress something, we must first let it fully expand." He who demands too much at once is acting precipitately, and because he attempts too much, he ends by succeeding in nothing.