He himself studied with many teachers. He assumed that each teacher was keeping secrets but that if he studied with enough of them he would get the secrets. This is because each individual teacher wouldn't know which secrets his other various teachers were keeping, and so there would be an overlap of material. Since what one teacher taught openly another teacher kept secret, he would eventually capture all the secrets in the overlap of material-- and this would be faster than waiting in subordination for one teacher to give up all his secrets.
I guess it worked.
I have heard that he summed up his martial arts knowledge into just a few phrases. One of them is: Xing bu po ti, li bu chu jian
Is anybody willing to venture a translation?
Update: the Chinese is now correct.