I know there is no such thing as an 'overnight success', but we have often referred to Matthew's 'switch'. One day, Matthew struggles with something, and the next, and the next, and the next, and so on. But then, on a random day, he can do whatever it was, like he's been doing it forever. It happened with crawling, walking, climbing up on the bed, talking, and now-- potty independence. Not yet perfected, but the 'switch' was flipped.