Square Fuseki is any Go opening where your first 4 stones form the perfect square shape. All sides have to be equal, all corners have to be 90 degrees. Minimum possible size is 2x2. Maximum is size of the board. It may be placed anywhere: in corner, on side, in center…
Both are squares and their centers are in tengen:
Corner square:
How did you get this inspiration?
Well, the go board itself is a perfect square…
… And of course, go by nature is a game of squares disguised as a game of circles and lines. 
Are diagonal squares counted?
I had a square fuseki played on me the other day - E14 x4 , then K16x2.
It did rattle me a bit until I calmed down and remembered that corners-sides-center does actually work 
Yes, that’s the one.
I will square with you that I am honored to be a Square Squire. (now all we need is a badge, a square medal and a secret society in a rectangular meeting place 
)
There is a mystery here. Do you have to interfere when someone goes for another strategy?
nothing actually work if opponent is higher ranked and has a lot of experience with their own unique fuseki
My idea is: it absolutely doesn’t matter which fuseki is more efficient when 2 even strength opponents play. Much more important is which fuseki lets you to improve faster.
The most easy to master fuseki is likely to look simple. What can be more simple than square?
Do you think this is easier to understand like for directions of play, so you can see better what you missed and improve on the next game?
This is what “rattled” means.
“Rattled” is when you panic in to thinking you need to interfere quickly to disrupt the strange new strategy, rather than just play calmly.
I was rattled by the apparent size of that huge square even though I know the answer to:
Who is winning:
I was so rattled I messed up the next fight 
But the difference between the inside and the outside was so great that I prevailed anyhow 
I think one of the fears presented by this fuseki is that white might do better than the picture above.
White has three spare stones, as you can see, so in reality as this unfolds white can press “out” into the sides. This is experienced when white starts playing the side star points after the square.
It’s scary trying to contain that… (at least for a basically-DDK).
Sane center square user would not limit himself to conquering the center only. He would attack corners and sides anyway.
If opponent wins, its because they are good at defending and counter-attacks, not because outside(corners and sides) is bigger.
What’s “sane” at one rank is “magical skill” at another.
I think your observation matches mine anyhow:
White has three spare stones, as you can see, so in reality as this unfolds white can press “out” into the sides.
This adds to the “pressure” that this fuseki applies - at least how I experienced it at my level.
This is like saying “there is no point in fuseki, the best player wins”.
I got that idea to keep following the prevalence of some theory but sometimes it seems to me that not allowing your opponent to get some perfectly placed structure may take prevalence.
Not because of fear, instead in a very logical way.
For example you may for some reason have to not pincer but after your opponent approach each of your corner and letting him take the middle edge hoshi will give him a favorable result so you accept to (double) pincer.
I have that feeling about the white tengen instead of taking the last corner in the diagram up.
It’s not rattled as you say, I mean it’s to not allow at some point a structure getting too perfect and go interfere in a analysed way, not under panic. I wonder
Well, there are players, I know many, who are reluctant to follow basic opening principles and ready to overplay as much as they can. We are used to think no this is not good, this can’t be, but it’s up to you to demonstrate it. This is not always as easy as it seems and furthermore maybe not the style of play in which you ll feel happy but that’s still part of the game.
Yes, and of course this is what I thought. I thought “oh, no you don’t you’re not having the whole middle”.
But my personal conclusion was that in this case I didn’t need to change my own strategy in this way. I feel that I would have been fine if I’d stuck with the “calm basic strategy” that I try to usually use. Not as a “rule that must never be broken”, but rather “in this particular case, I don’t think the square fuseki called for drastic change”.
Of course, what do I know? I’m just describing my experience of it.
O sorry I added another commentary meanwhile
Ok I got that on this situation you may have rattled in your opinion. I’m not sure myself about it anyway.
And I was opening a more global debate as that it’s not always rattling but at the opposite can be full of sense. Hard choice surely.
In this diagram putting a stone here at tengen makes 3 black stones in a kind of pincer. Like in a favorable position 2 for 1. So it makes sense and may be better as taking the last corner
