Don't get me wrong; modern autofocus systems are great. They nail the focus most of the time, including in challenging situations such as low lighting that gave most systems trouble even 5 years ago. They still struggle with, basically, "What really are you focusing on here?" In many cases guessing wrong by an inch or three doesn't matter, but close-up pictures shot with really wide aperture as with these flower photos are a situation where even a few millimeters count.