Technically, he wasn't the man he thought he was, because he wasn't the man he used to be. Circumstances, events, relationships had changed him into this new person; the person he was today. But then there was his identity. In his heart he knew himself to be Obi-Wan Kenobi, the great Jedi general of the Clone Wars, but in recent years he had become Ben Kenobi, hermit in the hills of the desert. And that identity was equally true. There were two sides of him now. Neither one was him, not exactly. But he wasn't these two identities combined either.
And that, of course, made him think of Anakin. How he had trusted and believed Anakin to be one person, only to realize that person didn't exist. And it would be easy for Obi-Wan to make the same mistakes and follow that path to darkness. And then who would he be? Certainly not the man he thought he was, or the man others believed him to be.
And it did worry him that the tendrils of doubt had already begun to work their way through him, laying the ground work for something dangerous in the future.