This is the sort of thing about which stronger players will say "That's obvious! You got to 3k without knowing that??" (either that, or they will say "That's wrong!"), but it's pretty basic and I somehow got to this point without realizing it.
We get told as early as beginner level that it's important to make a base. Probably "base" is more well defined than I've noticed (although I looked in a couple of John Fairbairn's Go Wisdom appendices and it's mentioned but not defined, so maybe the definition is too obvious to give!), but I always thought of it as "a bit of space on the side that can make an eye". My new realization is that, ceteris paribus, a single eye on the side is worse than no eyes on the side.
The first event in this journey was at a strong-kyu game review by Mateusz Surma at the US Go Congress last year, where someone's running group was making eye shape near the side, and Mateusz said (paraphrased) "if you're running to connect, just run, don't make eyes". That was new to me, but in retrospect it made total sense; you're going to end up alive anyway when you connect, so why make extra eyes you're not going to end up needing? So I filed it away as a special rule.
Then I recently watched an introductory lecture by Guo Juan about that most basic (sorry) example of a base, a two-space extension on the third line. One of her points was that if this group is hemmed in by opponent's stones on either side (say a one-space jump away), it's not only weak, but extremely inefficient. When your opponent makes all of their endgame moves, you're going to end up with a ton of your own stones surrounding only a couple of points.
Of course I am familiar with the topic of overconcentration, but to me it always meant a bunch of very strong stones enclosing only a moderate amount of territory. It didn't really occur to me that using six stones to take one point of territory (for example) is an even worse form of overconcentration!
So here's my new way of thinking. When getting a foothold on the side, unless you have the possibility of getting two eyes locally (or other factors are at play, such as a nearby weak group of your opponent, or you really think you need exactly one more eye), you're better off making sure that you are well equipped to develop into the center than making a "small" (one eye max) base. Your stick poking through your opponent's territory has already done enough damage by making your opponent place border stones on either side of it; in the case of a straight stick perpendicular to the side, you've taken away 3 points per row plus your opponent had to play twice as many stones as you locally. If you widen that stick, you're placing twice as many stones for a very small amount of extra points (a tiny bit of territory for you, a small reduction of your opponent's) without even ensuring life.
Here are a couple of examples. The first is a 3d Fox game I played recently:
- Click Here To Show Diagram Code
[go]$$c
$$ +---------------------------------------+
$$ | . . . . . . . . . T . T . . . . . . . |
$$ | . . . . . . . . . T . T . . . O . . . |
$$ | . . . O . . . W . X . a . O . . O . . |
$$ | . . . , . O . . . , . . . . . X . . . |
$$ | . . X . . . . . . . . . . . . . . O . |
$$ | . . . . . . . . . . . . . . . . X O . |
$$ | . . . . . . . . . . . . . . . . X . . |
$$ | . . X . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . X . . |
$$ | . . . , . . . . . , . . . . X , . . . |
$$ | . . . . . . . . . . . . . . . . O . . |
$$ | . . O . . . . . . . . . . O X X X . . |
$$ | . X O . . . . . . . . . . . O . O X . |
$$ | . X O . . . . . . . . . . O . . O X . |
$$ | . . X O . . . . . . . . . . . . X . . |
$$ | . . X O . . . . . , . . . . . X . . . |
$$ | . . X O . . . . . O . . . X . . . . . |
$$ | . X O O . . . . . . . . . . . . . . . |
$$ | . X . . . . . . . . . . . . . . . . . |
$$ +---------------------------------------+[/go]
As Black, I instinctively "made a base" with A. But KataGo thinks this move is pointless. White's groups on either side are strong, my single stone can easily run, so this is just points, and it's not very many points! I don't really want to play on all the triangled spots (eventually), but in that case why did I even start claiming this area? It's immensely more important to play on the lower side.
The second example comes from the game of another player who's a little stronger than me:
- Click Here To Show Diagram Code
[go]$$Wc
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . X X X . . . . . . . . . . . |
$$ | . . X X . O O . . . . . . . . X . . . |
$$ | . . O O O . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . 2 . 3 . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . X . a . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , O . . |
$$ | . . 1 . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . O . . . . . . . . . . . . O O . . |
$$ | . . . . . . . . . . . . . . . O X . . |
$$ | . . . O . . . . . , . . . . . , X . . |
$$ | . . . . . . . . . . . . . X . X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ +---------------------------------------+[/go]
After the 1-2-3 sequence, he was wondering how best to move out with his Black group. But my new principles got me wondering whether
was actually a good move in the first place. White's group at the top is plenty strong (things might be a little different if there were a Black stone at E17), so the move doesn't have much effect on it, and Black's not threatening to live on the side. Better to immediately jump out with something like A. KataGo agreed with me (although it only thought the 2-3 exchange lost a point or so).
I look forward to hearing whether this is actually as good a principle as it seems to me. I used to think that a stick poking into my opponent's territory is fine, a fully living group is great, and a narrow foothold on the side is somewhere in between. But it now feels like it is the worst of both worlds, a large commitment of stones without much profit either in points or in safety.