That can happen, but did you and your opponent keep missing it for 60 moves?
for 63
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Well, Iāll be happy to reach my best as the worst of yāall. 
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C10 is a fairly normal opening move. Itās a big point.
Itās not that C10 was such a bad move, it was the timing that was bad (or dubious at least). It violated the principle of āurgent moves before big movesā. The upper left corner area is an urgent area after white A.
White A is a non-joseki move, but deviating from joseki isnāt neccessarily a bad move. In this case whiteās shape is a bit weaker than usual.
It doesnāt even matter much if you know that white deviated from joseki, as long as you realise that white A is putting pressure on blackās corner group by blocking a potential escape route towards the upper side.
If white is allowed to follow up with B, blocking blackās other escape route, blackās corner group becomes completely sealed in and blackās eye space is even quite restricted. Blackās corner group would immediately be put on the back foot.
And when white is done harassing blackās corner group, he can shift his attention to the next target: pressing blackās now baseless C10 stone towards whiteās C15-D15 wall, all the while keeping the initiative by harrasing blackās unsettled groups.
So it is quite urgent for black to prevent white blocking at B and sealing black in (maybe even in sente). The natural way to prevent that is jumping out along the left side. C14 or B14 would do the job. And those moves would have the added benefit of also reducing any potential white might have been hoping for on the left side (just as I assume black intended with C10), killing 2 birds with 1 stone.
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My idea was that because of the less pressure put by A on the corner, playing C10 looked a bit more like an alternative.
I agree that when white chose to focus on the upper side with A, itās natural for black to focus on the left side. I assume that this was the aim of C10.
And C10 would be fine if whiteās block at C15 wasnāt so severe.
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hope this helps. If you want more reviews in the future, Iām always happy to help.
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Thank you, I will read it carefully 
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Sorry if itās a little messy. And I do think that you did well going against a player six ranks above you. white made his fair share of mistakes in that game too.
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