Why did the Doctor run away from Gallifrey?

This has been on my mind recently. What are people's thoughts on this?

Bored, or got tired of seeing people suffer when the Timelords could be helping were my two favorite ideas.

Ronpur wrote:

Bored, or got tired of seeing people suffer when the Timelords could be helping were my two favorite ideas.

I like the boredom idea. Simply because at first, Hartnell's Doctor clearly doesn't really care about the universe around him. In fact, for the first couple of Hartnell's seasons all they do is travel, get stuck in a mess and runaway again. They don't stick around and seek to help as such until about half way through Hartnell's run when he seems to have become more of a hero than just a passer-by.

So I kinda like the idea that he was bored sickless of the Time Lords having so much power and ability and doing nothing with it, just watching the universe pass. So he runs away simply to get away, but then, as we see, he begins to realise the evil in the universe and seeks to fight it and save people.

Could also be something to do with the Doctor's 'selfish thirst for knowledge' that Pertwee talks about in Planet of Spiders?