I think what Lucas was getting at was that Anakin missed an intergral part of his training, the part that Yoda does while the would-be Jedi are still young. Anakin went right from being a slave to a Padawan, he completly skipped past the process that filters out any potential dark-siders, so Obi-Wan had to give the initial training as well as the Padawan training, so maybe it was the initial training that Obi-Wan had failed in, not the Padawn training, hence the line " I thought I could train him as well as Yoda trained me"