When you blow air with your mouth wide open as big as you can it spreads out and loses its power before it can reach your hand at the end of your outstretched arm. But blow air with puckered lips and it keeps its focus all the way out to that same hand.
I have learned from my photographer BFF, ladyhawker, that the same is true when setting the aperture on your camera. A large aperture might give a wider shot but the depth of field is more shallow. And, in contrast, a smaller aperture will give a deep depth of field.
I have had to learn this truth over and over in my personal life. Keep my eye on the prize. Keep my focus. I want that hand to feel my warm breath.