Note: Based on the last two arcs of Astonishing X-men, so there are minor spoilers. I'm treating this aspect of the story as canon, just assuming it took place some time ago (before Messiah Complex)
It's a beautiful lie
It's the perfect denial
Such a beautiful lie to believe in
Scott had always believed his powers were beyond his control. It was a simple thing to believe, and with all the complexities of his life, there was an obvious virtue to simplicity. When he opened his eyes, the force blasts streamed out, seemingly of their own will. Occam's razor said, the most straightforward answer was the right one -- and so no one ever looked for another. Not his mentor Charles Xavier, who taught him to control and contain his power; not Sinister or Apocalypse or Magneto, or any of the nemeses who ever sought to use it for their own ends.
And not Jean. Not even when she was Phoenix, attuned with all the powers in the universe and utterly at one with his mind. Once and only once, Phoenix-Jean offered him the chance to hold his power in, to be together with nothing between them. He thought he was seeing clearly for the first time. Neither of them realized they were only building on the foundation of the same old lie.
It was such a perfect lie that Scott didn't even realize he was telling it. It was such a perfect lie, no one ever looked for the truth.
Until there was Emma. Whatever her intentions, she was able to cut through the lies he didn't even know he was telling. Neither of them knew what it meant, or where it might take him next. If he wasn't careful, it would be easy enough to fall into the old patterns. But that moment of clarity, brief though it might have been, couldn't be denied.
He could go back to telling the old lies, but he would never be able to believe them.