I thought the same thing but it really makes sense. The second you start going into anything challenging...your retention drops off a cliff. For Udacity, they h

I thought the same thing but it really makes sense. The second you start going into anything challenging...your retention drops off a cliff. For Udacity, they have to give the illusion that MOOCs have high retention rates (because everyone criticizes them for low retention). If you don't believe me then just go on youtube and look for some Stanford, MIT etc. course where they uploaded all the lectures. You'll see the first lecture has lots of view but if you scroll through the rest you'll see the retention drops significantly. I've ran some numbers on this and it turns out the biggest drop is actually in the second lecture.