DS is just over 3 and a delightful yet stubborn child. He just doesn't want to use the potty. We've tried reward charts, picking his own potty, picking his own pants, books about potty training, being completely positive about the whole thing, full of support and encouragement about how clever he is. He seems excited with us but as soon as the day gets underway and you ask him to use the potty is "no!" And he gets stressed about it. I have no idea what I'm doing wrong.