perception.
Why This Puzzle Is So Deceptively Hard
Most people assume that distinguishing between a lowercase “b” and a lowercase “d” should be effortless.
After all, they’re different letters.
The problem is that they are also mirror-like opposites.
A lowercase “b” has its vertical stem on the left side.
A lowercase “d” has its vertical stem on the right side.
When viewed individually, the difference is obvious.
However, when dozens or even hundreds of similar letters are packed together into a grid, your brain stops examining each character individually.
Instead,
