Seems like every day a new one of these arrives...purchased with gift money from the holidays. Every day, he works to solve new puzzles. And once they are solved, he challenges himself to get faster and faster.
He tackles them with energy, focus, and perseverance. The payoff for me: the sound of his squeals of joy when he solves a new one or beats his time, his delight as he revels in the payoff of hard work. Reminds me to celebrate more...the little things as well as the big.