mind can only tolerate what the butt can. Also, a child's attention span is only good for 1 minute per year and peaks out at 15 minutes. That means you really only have an adults attention at most 15 minutes before the mind wanders.That said, it doesn't mean you have to stop. Switch gears for a minute then go back. As a teacher, I lecture 10-15 minutes then students might debate a point for a minute or students work a problem on the board for a minute or two. Guess what, go back to lecture and the 15 minutes starts over. Switch gears and then go back.Think church, doing an illustration, add a time of pondering or soul searching then go back to the sermon...your 15 minutes begins again.That said, I have sat under bible teachers where 90 minutes of straight one directional teaching had me the whole time but understand, this was not weekly church and was more of a church conference.