they can pause and repeat their cousin, without feeling like they're wasting my time. if they have to review something that they should have learned a couple of weeks ago, or maybe a couple of years ago, they don't have to be embarrassed and ask their cousin. they can just watch those videos; if they're bored, they can go ahead. they can watch at their own time and pace. probably the least-appreciated aspect of this is the notion that the very first time that you're trying to get your brain around a new concept, the very last thing you need is another human being saying, "do you understand this?" and 