Order is a separate problem from position
Two things have to be held at once here: which squares, and in what order. They fail independently. A common experience at higher levels is knowing with certainty that the pattern used the top-left, the centre and the bottom-right, and having no idea which came second. That is not a partial memory of the sequence — it is a complete memory of the set with the ordering lost, and it is a well-documented way for serial memory to break down.
The structure is the same as the Corsi block task used in psychology, where a tester taps blocks and the subject taps them back. The version here differs in one important respect, covered below, and that difference makes the levels easier than a Corsi span would be.
The pattern grows rather than restarting
Every level keeps the previous pattern intact and adds one square at the end. That means the opening squares are shown again at every single level, so by level six the first three have been rehearsed six times and are effectively free. All your capacity goes to the tail.
The consequence is a specific failure mode: an early square you learned sloppily stays wrong forever, and it will end the run several levels later, while you are concentrating on the new material and reciting the opening on autopilot. Getting the first three or four genuinely solid, even at the cost of looking slow, is what separates a level 4 run from a level 10 run. It also means the level number here is not comparable with a test that shows a fresh pattern each round — the numbers here will be higher for the same person.
Two things that reliably help
The first is turning the path into a shape. Rather than nine positions, see the sequence as a movement: down the left side, cut across, back up the middle. A shape is one item; five positions are five.
The second is numbering the grid like a phone keypad and reading the sequence as a number, which converts a spatial problem into a verbal one you can rehearse under your breath. Whether that helps depends on the person — some find the two codes interfere and do worse. Faster flash speeds also suit some people better than slower ones, because a slow pattern has to be held for longer before you can start clicking. The settings are there to be tried in both directions rather than left at the default.
Questions people ask
Can the same square flash twice in a row?
No. Two consecutive flashes of one square are hard to tell apart from a single long flash, so the next square is always chosen from the other eight. The same square can certainly appear again after a gap, and often does.
What happens if I click while the pattern is playing?
Nothing. Input is only accepted once the status line says to click it back. This is deliberate: it means you can rest a finger over a square you are worried about forgetting without any risk of registering it early.
Why does the level number differ from other versions of this game?
Because implementations differ in whether the pattern is rebuilt each round or extended. This one extends, which makes the same level easier to reach. There are also versions that add a sound per square, giving you a second channel to remember it on and raising scores again. Compare like with like, or only against your own earlier runs.
Is the grid always three by three?
Yes. Nine squares keeps every position distinguishable at a glance, which is the point — a larger grid starts testing whether you can locate a square accurately rather than whether you remembered it.