right but you left out that me walking to any grain of sand is a huge factor slower than having 1000 super fast pc's grinding out try after try after try.
Picture my analogy for a moment. Even if you had 1000 super-duper fast PC, trying 1 quadrillion private keys per second, you would only manage to find 0.013% of the grains of sand per second, for one planet Earth. It'd take you 7501 seconds, or about an hour and a quarter to find all grains of sand in one planet Earth, and you'd still have 999,999,999,999 planets left; it'd take more than 43 trillion days to cover just half of the total grains.
And after 86 trillion days, in glory and triumph, you'd have successfully searched 0.000000000000000000000000000000000000000000003% of the total private keys.