Well, also the situations involved. Other than Snape, the Dursleys, possibly Lockhart, and the Basilisk (hey - if God can be Geassed, then so can a measly reptile), there aren't a lot of people I could seriously see Harry Geassing in years one and two.
Come years three and four, however, I can see him Geassing the truth about his parents' betrayal out of Sirius or Peter, being more active in the Triwizard Tournament... and come year five, that's when everything would go completely Off the Rails
, given my plan. However, that particular plan can't come into fruition without the Geass of Command that Lelouch has. The only other way I can think of to achieve it is with Charles' Geass that lets him rewrite memories, and it's nowhere near as surefire as Lelouch's Compelling Voice
On the subject of not being a genius, there is
that, but remember that he has Hermione for that, if he decides to let her in on it.
edited 1st Oct '12 12:04:22 PM by EvaUnit01