1. All wind and currents circulate within specific areas of the ocean. There is no current or wind that travels all around the world.
   • Polynesian and Micronesian sailors followed winds and currents in the Pacific Ocean that ended at the edge of New Guinea, just beyond the reach of China. Therefore Chinese sailors never traveled the Pacific. Nor did Polynesians sail in the South China Sea
   • Indian Ocean sailors could sail from the east coast of Africa to India, but they could not pass the Mozambique channel with its deadly Agulhas current. Therefore even the southern part of the Indian Ocean was unexplored..
2. Coastal shelves are also limited to specific regions.
   • Europeans managed to sail in the northern latitudes using the coastal shelf, but could not travel the South Atlantic where there was no significant coastal shelf.
   • Chinese and Southeast Asians could travel the South China Sea, but not the Pacific Ocean where there are no land masses, and therefore no coastal shelves.

Traditional navigators all knew how to sail in bounded regions, but none could sail beyond their own locale.