I learned a lot in creating these videos during my transformation from professor to popularizer. You see, in a classroom, we have a captive audience. We can give a boring lecture and the students are not going anywhere. However, YouTube videos must compete for a student's attention. They are probably media-multitasking (i.e. updating their Facebook status and tweeting at the same time), so you've got to make the videos compelling.
Via Dennis T OConnor