Point out one example. Evan Tanner, former UFC Middleweight champ, taught himself grappling from dvds. Him and his training partners would watch them and then drill them over and over.
Ah but as you say, he and his training partners, I was asking how one can do it all on one's own. He was already a wrestler so watching BJJ moves and making them work was relatively easy for him having down an allied art before.