Think of it like the double haul.
One of the toughest bad habits we often pick up in Spey Casting is engaging the top hand, or what we call “Top Hand Push.” It’s easy to start since we often also do this as single-hand casters when casting single-hand rods. In both cases, it’s not good mechanics nor generally desired. But have you ever thought of the bottom hand in spey casting like a double haul?