When photographing wildlife very often speed is critical. You've likely experienced the frustration of missing focus on fast-moving animals, even with high-end telephoto lenses and the latest camera systems. And the worse situation is when your autofocus is stuck on the background and refuses to jump back and lock into a subject just in front of you. This happens especially with the longest focal lengths, as the foreground can sometimes be so blurred that the camera’s brain can’t recognize a subject close to us.