When I play blitz games or have to play fast I always make very simple mistakes like "I'll capture that group with my next move", it's his turn and he captures mine. That or similar mistakes (overlooking atari) happen in almost each game when I have to play fast. I always think there were some liberty left or he had one less. How can you reduce such blunders? I'm not a beginner. Just play a lot of blitz games?

Bill Spight: I have the sequence read out, play it out and suddenly he captures my stones.

daal: Theoretically I should be good enough to see those things at a glance. I just somehow overlook it.

I'm normally very cautious and recalculate everything multiple times after each move.

Ah! That is something that Kotov warns against. His recommendation is to read each variation (that you do read) only once. And then trust your reading.

What may be happening is that, because you check and recheck yourself in non-blitz games, you can afford to be careless the first time, so you are. And then in blitz games, where you cannot check yourself, your carelessness shows.

Tommy Armour, the golf champion, said of the amateur golf practice of taking a Mulligan, "A cow could do it right the second time."

You might try, in regular games, Kotov's advice. Read each branch that you decide to read only once. Adding time pressure to that exercise would probably make it more difficult, so it is probably better to stick to regular games until you can do that.

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Edit: BTW, that does not mean that once you have read a line of play and your opponent makes the next play on that line, that you just go ahead and make the next play without reflection. It is fine, and normally desirable, to read afresh at each turn. Even a variation that you have read before.

Ok I'll try. I should do the same with tsumego, right? When I do them, even very easy ones, I recalculate everything multiple times. Maybe because of the advice that one should be 100% sure about the solution.

daal: Theoretically I should be good enough to see those things at a glance. I just somehow overlook it.

I'm just about convinced that studying the game itself helps very little. Surgeons study for a decade before being allowed to operate on people, and surely one of the things they have learned is "don't forget anything inside the patient", yet it still happens. There is a class of errors that are not borne out of ignorance.