As a kid, I learned the very basics of juggling from John Cassidy's classic Juggling for the Complete Klutz. I can still (barely) keep three balls aloft for about 15 seconds today, just enough to pretend that I "know" how to juggle. I recall that one of the first tips in the book is to practice standing in front of a wall. That's because juggling is really all about the balls moving up and down and side to side but never away from or towards you. (Standing in front of a wall also keeps the balls from flying everywhere as you're learning.) Watching Taylor Glenn juggling from above delivers a terrific shift in perspective that reveals why juggling is really a two-dimensional art form. Slow motion clip below! And here's another video of Glenn juggling from above.
And here it is in slow motion: