Later, he will say it was a calculated choice, that he looked at the odds and looked at the clones and decided that better the Jedi he didn't know than the Sith he did. This is, as it happens, a bare faced lie. (or: A Sith Lord realises, abruptly and rather late, that war means casualties, and decides that the great Jedi genocide plan can go fuck itself.)

Obi-wan Kenobi was chosen by a Master when he was a few months shy of his tenth birthday. Twenty plus years later, the galaxy as a whole has rather a lot of cause to regret that. (The longer the war drags on, the more Qui-gon Jinn finds to question; about himself, about the events of history, and about the Sith Lord who was once Jedi Knight Obi-wan Kenobi.)