Don't defend what is not yours
This is an example of an opening where Black is often tempted to defend what is not his - and where he loses if he does so.
If Black tries to both defend his corner and expand the top from his left side wall, he ends up with 2 relatively weak groups.
If Black wants the corner, he should defend the corner, if he wants to extend the top side, approach from the left, but doing both in this case is unreasonable.
After , white can aim for either of the 'a's - or other plays into the corner or top side, depending on the remainder of the board. Black cannot defend against both these and will take a loss on at least one side.
is something of a double purpose move since it extends from and induces and .
It is important to understand that a komoku such as in the top right does not aim at capturing the corner, but is intended to build a shimari and an extension from it. Even without the shimari, the Black extension with is good for black.
tapir: Basically, the left corner looks good for white, white has stable territory black has a wall, but doesn't secure anything, so black needs an extension. If the pincer aims to be that extension it shouldn't be so near to get so weak as to invite a counterpincer or shoulderhit - as you can't care about both corner and pincer stone. But this is only my thought, stronger players should tell sth. as well. Black may be satisfied after in the line without attachment, probably White at b next, White may go directly at c with ... Blacks wall doesn't accomplish much here.
tapir: My contribution is now cut into two parts and changed the order. That is all fine, but it would be great if the text is adapted accordingly. To me it isn't completely clear what this page should end up, the 2nd diagram is pure ill-prepared aggression, the now 4th diagram argues that even the close pincer might be too aggressive / close here as it is weakened by the white stones and likely requires reinforcement later on, 3rd diagram gives an alternative (that I believe is good) which doesn't need later reinforcement on the top side. To go even further I would play the distant low approach to begin with if I were playing White to discourage a Black double purpose pincer. But all this is more general discussion of the position than illustration of a single principle.
Morten: Sure, Diagram 3 shows the 'baseline' play which in most cases (?) would make sense, Diagram 2 should be avoided. Should be emphasised. Whether is a good approach is another discussion. I left your contribution next to the diagram where it was, no? But I am not quite sure what Diagram 4 is trying to show - I also think the close pincer is too close.
The main message of the page is what is says in the title. In this case, if black mistakenly believes that both the upper side and the corner are 'his' due to his wall on the left and the komoku stone, he is wrong - and if he tries to play to defend both, he will lose. Maybe, instead of adding detail to the example given, we should add another example which also (or better) illustrates the point.
tapir: Both dia 3 and 4 are by me, originally in the different order. Now the text next to diagram 4 makes precious little sense. If the page is defined by the page title then it needs a second example. The lengthy discussion of approach, pincer etc. can imo be moved to a BQM.
tapir: I had several good examples for "mistakes due to killing intent" in handicap games yesterday - killing intent in this case meant stopping to check your own eyeshape when you spot and attack an a weak group of your enemy - i.e. more general and not at all opening specific. Don't defend what isn't yours, might be too timid - defending is often bad even where you defend what is yours, isn't it?