You can have the greatest gear in the world, with a digital cinema camera, great lighting, and a high end post system. You can have a huge crew of experts that are craftsmen in their trade. You can study your camera and gain experience until you're prepared for just about any type of shot. But without good talent that can take direction, you're going to have a hard time seeing your vision realized. Taking the extra time to audition a wide pool of people to get the right fit is worth it, and trusting your gut when you're selecting someone can make or break your project.
I've worked with reluctant amateurs and paid professionals, and seeing a great performance can inspire the whole crew to work a little harder, stay a little longer, and talk up the project when they finally go home. Plus, if you're talent is nailing the performance every time, it opens up more creative options while you're shooting. Attempting a complex shot when you need 20 takes just to get the line right can be really frustrating and time consuming. I'm a firm believer that people are born with predispositions (call it genetics if you want to get scientific) to be good at certain things, and that books and practice only take you so far. Look for that intangible quality in your talent that can translate to the screen.
Sometimes people with great personalities just don't come across on the same way on camera, so always do a screen test before you decide. When you're on set, work hard to develop and maintain a good rapport with your talent. Knowing when to push, and when to give them some room takes practice, and every person has their own unique personality you'll have to adapt to. It's part of the challenge, and part of the fun of producing great video.