Perhaps Donna is the reason he now knows there is no such thing an an unimportant person.

"Rule 1: The Doctor Lies" = Moffat's copout answer to practically everything.

that's not called a mistake. it's called CHARACTER DEVELOPMENT!

Rule #1: The Doctor lies.

It's not a mistake, it's that he was upset Rose was gone at the time and he didn't wanna be bothered by someone he thought to be annoying at the time.

Ya but...Donna Noble was the most important woman in the UNIVERSE and whole of CREATION. so....yup

10 said it in a different context, whereas if she was wanted by some Master Race of Aliens then she'll be important to them, that's the context he's implying, and when he said Wilf is not remotely important, he was being sarcastic, just to clear that up with people :) 

It had nothing to do with Donna's actual importance and everything to do with the personalities of 10 and 11.

That was actually an important scene, that was why he kept telling her she was brilliant and amazing and everything, because he realised that in that moment, when he was bitter because of losing Rose, he was a part of giving Donna that shitty image she has of herself for the sake of a quip or a thoughtless remark... we know she is important, the most important, in fact, so it does add up.

Except she turned out to be the most important woman in the universe sooooo...

And he spent the rest of his time with Donna telling and convincing her how important and brilliant she was. The poor guy had just lost Rose, his usual bedside manner was a little lacking but he spent the rest of his time trying to make it up to her :)

Later on she was important so....BOOM

But then Donna turned out to be the most important woman in the whole of creation, so...

It was that he learned from thinking Donna was not important that everybody in the universe is important.

Love it when people are like "character devlopment!" or "difference of personalities" come on guys let's face it, it's just Steven Moffat contradicting Russel T Davies.