Harry's down to his shirt as well, doublet and jerkin tossed carelessly into a corner.

Though he is composed almost entirely reckless impulsiveness-- named for it, after all-- Harry is able to muster discipline in at least one area of his life, and it is this. His eagerness may suggest he wants to dive right in to just whacking people with sticks, but in fact, he will take his time to be taught the unfamiliar forms, and listen attentively to the basics.