It’s not meta: that’s really a screenshot from Paint.net; read on, to find out why I’m playing a game in a graphics program.
It’s not trial and error, in the conventional sense, at least; it’s proof by contradiction: hypothesizing that a certain cell has a certain status, and unfolding the consequences logically, is shown to lead to absurd conclusions, hence falsifying the hypothesis => it follows that that cell must have the opposite status.
If the game allowed taking annotations, I could find the solution without having to use pen and paper, or a program. That’s what’s “wrong” with it.
Though I can’t say whether it’s a deliberate design decision, I’m inclined to think not, because the use of pen and paper while playing computer games is a time honored tradition, and besides, the designer can do absolutely nothing about it.
Since I’m hardly at my freshest when playing HexCells, and the ambient music does not help keeping me awake, my eyes tend to get crossed if the unfolding process is longer than some.
OTOH, I’m also not positive that the player is “supposed” to use that kind of solving; chances are I’ve missed some other, more obvious clue; it happens to me all the time in HexCells.