The point, though, is that in the very best street photos, there is a strong element of serendipity. Our methods, our skills and talents, can produce work that is only so good. Only by making a lot of that work, and by embracing the possibility of luck, do we occasionally produce greatness.
This, I believe, is what HCB means. Skill and talent surely must be there. But also there must be luck. In the greatest pictures, there is always luck.
Also, I think you are completely on the wrong track to propose that mastery tends toward unconscious activity. Surely, for the trivia of the work. Setting the shutter speed, mixing the plaster, kneading the dough, we don't think much of it. But for mastery we need to strive to be conscious of what matters. If we slide and are unconscious of the texture of the dough as we knead, our bread becomes mediocre. It seems inconceivable that HCB was not intensely conscious of what was in the frame. But still it's luck. It's always luck. And then the word he leaves out: too.
