The thing about orbits, about loops, is they always circle around. As Don forgives fate and releases his burden, the deadly obsession settles inexorably into Leo's own gravity well.
His skills don't tend towards research and calculus, but he trains and strategizes with single-minded focus. He becomes increasingly paranoid, treating everything as a threat. He's hostile to his own family, as though their failure to achieve the skill level he demands from them is itself some kind of amorphous enemy.
His desire to protect his loved ones, even from themselves, becomes uncontrollable.
The outcome is as predictable as an eclipse.