Why is a low completion rate causing concern? I never completed the machine learning course by Andrew Ng - my schedule didn't always wind up aligning with the t

Why is a low completion rate causing concern? I never completed the machine learning course by Andrew Ng - my schedule didn't always wind up aligning with the times allotted for homework, and to be honest, there was some laziness mixed in there later on as well. I still got a lot out of the course - I've unexpectedly found myself having to do a lot of machine learning work at my new job, and the stuff I was exposed to in the Coursera course has helped to orient me. A couple comments on that page stood out for me - one, that even with a low completion rate, more people completed a single online electronics course at MITx than have ever done so in person in the entire history of MIT. Second, the comment likening MOOCs to books - even if I don't finish a book, I still get value from reading it.