Mindpower is basically the amount of principles you can have... Players start out as mp3, so they can pick 3 principles in the story the first time around. If you have 2, or actually 2/3, that means you've picked two principles already. You will get the last mindpower when you pick the last principle in your story, making it 3/3.
Unless there's some sort of bug. o_o I heard earlier that Manu was considering making the first mindpower for newbies smaller, either 1 or 2, but he definitely would've announced that. In the worst case scenario, you can reset the account since you haven't really done much except the tutorial part.
Once you finish the story you can replay it, picking another principle and getting into mp4.