I saw the importance of knowing stuff illustrated vividly yesterday afternoon in a game that two of my friends were playing together. They shall both remain nameless here.
White was way ahead and he won the game easily, but could have won by a landslide if some vital information about the bulky five had been seared into his memory. White had attacked a black group and reduced it to a bulky five. There was also a false eye attached to the bulky five, and there a miai situation which insured that the false eye could never be real. After making the placement on the vital point of the bulky five, white could have used his next move to insure the isolation of the group. Black would have needed two moves in a row inside the bulky five to make two eyes after the killing placement. He could never get those two moves in a row. But rather than insuring the separation, white added a move inside the bulky five. This was essentially a pass. Black went on to secure a connection for his formerly dead bulky five shape to another live group. I imagine that there was wailing and gnashing of teeth after that.
White was in byo yomi, which of course makes it hard to think clearly. All the more reason, however, for having as much "stuff" seared into one's memory as possible ... stuff you don't need to think about, not for a minute, not for even ten seconds.
I had fun watching that game because I saw this situation, and I knew the instant that the second stone went down into the bulky five that it was no better than a pass. How exciting. White, by the way, is a great player and gave me a trashing the week before. So I ask myself, what obvious things do I not know? What "pass moves" do I make each day because I lack that critical knowledge? What do I have to think twice about that will steal critical seconds when I am in byo yomi, which is more likely to occur now that I can actually read far enough ahead to start using up my time in the middle game?
I have to do more tsumego, and I have to learn more positions by heart... L, L+1, L+2. I have said before that I want to not only know their status, which I do, but know every likely attack, and proper refutation.
I am going to be a go player yet, and knowing stuff is going to help to get me there.