Why do we surround the corner in go?

Question

After watching several tutorials, everyone says to surround the corners. I was wondering why you do this? If I start playing the corners, how do I combat white if they instead start to only develop in one area, like below, with white's plan being playing R-13, R-14, R-15, R-16, S-16, and T-16, and then forming eyes making it an unconquerable string, as shown with the highlighted pieces.

$$Bc
$$ -----------------------------------------
$$ - . . . . . . . . . . . . . . . . . . . -
$$ - . . . . . . . . . . . . . . . . . . . -
$$ - . . . . . . . . . . . . . . . . . . . -
$$ - . . . . . . . . . . . . . . . 1 W W W -
$$ - . . . . . . . . . . . . . . . . W . . -
$$ - . . . . . . . . . . . . . . . . W W W -
$$ - . . . . . . . . . . . . . . . . W . . -
$$ - . . . . . . . . . . . . . . . . 6 4 2 -
$$ - . . . . . . . . . . . . . . . . . . . -
$$ - . . . . . . . . . . . . . . . . 5 . . -
$$ - . . . . . . . . . . . . . . . . . . . -
$$ - . . . . . . . . . . . . . . . . . . . -
$$ - . . . . . . . . . . . . . . . . . . . -
$$ - . . . . . . . . . . . . . . . . . . . -
$$ - . . . . . . . . . . . . . . . . . . . -
$$ - . . . . . . . . . . . . . . . . . . . -
$$ - . . . . . . . . . . . . . . . 3 . . . -
$$ - . . . . . . . . . . . . . . . . . . . -
$$ - . . . . . . . . . . . . . . . . . . . -
$$ -----------------------------------------

I have a couple of questions from this:

1. Can I prevent white from making these strings, and how?
2. If the answer for 1 is yes, then will the game be just black repeatedly stopping white?
3. From 2, if that is also yes, then how do I take more territory so I can win?
4. Next, if white's move is bad, what can I do to use it to my advantage? How is it bad?

Please provide as detailed answers as possible, and possible game variations and mistakes from both sides, thanks in advance.

Answer 1

It's entirely a question of efficiency: It simply takes fewer stones to secure more territory if you play in the corner.

Taking, for example, the eleven stones White plays in your sample game, if Black had played the same number of stones in the corner instead:

$$Bc
$$ -----------------------------------------
$$ - x X . . . . . . . . . . . . . . . . . -
$$ - x X . . . . . . . . . . . . . . . . . -
$$ - x X . . . . . . . . . . . . . . . . . -
$$ - X X . , . . . . . , . . . . . , O O O -
$$ - x X . . . . . . . . . . . . . . O x x -
$$ - x X . . . . . . . . . . . . . . O O O -
$$ - x X . . . . . . . . . . . . . . O x x -
$$ - x X . . . . . . . . . . . . . . O O O -
$$ - X X . . . . . . . . . . . . . . . . . -

Same number of stones, same basic unkillable shape with guaranteed eyespace, but Black now has 7 points of territory surrounded compared to White's 4. For the same number of turns, this is definitely advantage Black.

Alternatively, if Black were to use the same shape to capture the same number of points in the corner:

$$Bc
$$ -----------------------------------------
$$ - x x X . . . . . . . . . . . . . . . . -
$$ - X X X . . . . . . . . . . . . . . . . -
$$ - x x X . . . . . . . . . . . . . . . . -
$$ - X X X , . . . . . , . . . . . , O O O -
$$ - . . . . . . . . . . . . . . . . O x x -
$$ - . . . . . . . . . . . . . . . . O O O -
$$ - . . . . . . . . . . . . . . . . O x x -
$$ - . . . . . . . . . . . . . . . . O O O -
$$ - . . . . . . . . . . . . . . . . . . . -

That's 4 points each for Black and White, but Black only took eight turns whereas White took eleven. That means Black had three whole turns to go and do whatever to get even more points anywhere else on the board. Again: Advantage Black.

Can you prevent White from making these live shapes on the side? Maybe. Depending on how the game plays out, there's probably plenty of opportunity to disrupt it before it becomes unkillable. But the real question, the one you're not asking, is should you?

And the answer to that is…also maybe. The whole point of Go is to have more territory than your opponent at the end of the game. Sometimes that means killing their shapes so they can't get points, but sometimes that also means just letting them have their points while you try to make more points somewhere else. A score of 1-0 is just as much a win as a score of 100-99.

How aggressive or how passive you should be during a game really depends on the situation on the board, not to mention your own personal playstyle, and the question on when you should attack and when you should defend is pretty much the core of all Go strategy and far too complex to get into here.

But in general, if your opponent insists on spending more stones to secure less territory, you should be happy just taking the easy points somewhere else.

Answer 2

It is a question of efficiency. In this diagram, white has indeed made a live group, taking 11 moves to surround 4 points of territory. The black stones 3 and 5 make a loose but significant claim to 30 points or more. If black had been making similar moves with the other nine plays while what was building its little fortress, it would have a much more secure and larger network in place. The prospect is for a sizable black win.

More specifically about corner play, in a corner the edges of the board surround a territory on two sides, leaving a player to build walls only along the other two. Along the edge, the board provides 1 side, leaving the player to form three sides. In the center, the player must form all four sides. Thus only half as many moves can claim equivalent territory in a corner compared to in the center. Also, an invasion of a corner is more easily squeezed against the edge, if players are of roughly equal skill.

Generally a god player starts by developing a loose network of stones, and as play progresses these get closer and tighter, with gaps filled in. The details vary widely, of course.

Answer 3

The answers by goldPseudo and David Siegel say most of it.

I should just like to add these positions, namely three groups which can be expected to live unless White gets in a lot of moves very close around them before Black answers:

$$Bc
$$ -----------------------------------------
$$ - a a . . . . . . . . b b . . . . . . . -
$$ - a a . . . . . . . . b b . . . . . . . -
$$ - . . X . . . . . . X . . X . . . . . . -
$$ - . . . , . . . . . , . . . . . , . . . -
$$ - . . . . . . . . . . . . . . . . . . . -
$$ - . . . . . . . . . . . . . . . . . . . -
$$ - . . . . . . . . . . . . . . . . . . . -
$$ - . . . . X . . X . . . . . . . . . . . -
$$ - . . . . . c c . . . . . . . . . . . . -
$$ - . . . , . c c . . , . . . . . , . . . -
$$ - . . . . X . . X . . . . . . . . . . . -
$$ - . . . . . . . . . . . . . . . . . . . -

The a group is a standard position, taking the corner by playing at the 3-3 point and the b group is also very common, usually referred to as a base. These are both essential building blocks in the early stage of sketching out positions. The c group, however is not a standard shape, and I have a much sketchier idea of when it is alive.

As in the previous examples, we see how much more efficient it is to make a safe group in the corner (1 move) as against the side (2) or centre (4?),