Mercury Fluid Links
It’s pretty clear how the Ninth Doctor had to die for his sins (speaking in a narrative sense) in order to be forgiven and reborn. Heck, primarily just to forgive himself by becoming a completely different person. The problem is, though the Ninth Doctor was a right bastard at times — careless even — he was guilty as hell about it, and the past effects of his arrogance. He just couldn’t help his behavior. He spent his whole “life” trying to compensate for it. Now the Tenth Doctor is a new man. He’s cast off that weight, and isn’t beating himself up anymore. He feels free to do whatever he wants. And that means pulling out all the stops the Ninth Doctor had on him — acting like he’s got a sort of a mandate, now that he’s been reborn. Yeehaw, nobody can stop me now! Top o’ the world! It’s like he hasn’t really learned at all. Nine hundred years of phone box travel, and he’s still a little boy.
That has to be set off somehow. He has to seriously grow, as a person. And it looks like that’s what Davies is doing, this series — especially with the “questioning beliefs” business in The Satan Pit and elsewhere, and being forced to confront Sarah Jane and other issues. It’s like a road lined with signposts saying “slow down; curve ahead”. And if he doesn’t heed them — well. He’ll learn sooner or later.