Hitomezashi
Running stitches along every row and column, each starting a half step in or not. The boxes and crosses that appear were never stitched.
About this pattern
Japanese sashiko stitching · one-stitch pattern
The whole rule is one bit a line: a row of dashes either starts on the stitch or on the gap, and so does every column. Nothing decides what happens where they cross, and yet the sheet fills with closed boxes, long staircases and rivers that wander through it. The figure belongs to the interference between two sets of choices, which is why looking for it in any single stitch never finds it.