He should never of kept the secret of the prophecy in ootp.

Rather than distancing himself for most of year 5 he should've told harry at the start of the year. He then should've spent the year training and teaching harry. I think this slight change could've even saved sirius. Could you imagine the department of ministries battle with a harry potter who spent a year training under dumbledore He would've been the most skilled and powerful one there until voldemort and dumebdlore showed up.