Most of the time, I can see right through the illusions. We’ve seen the impossible trident, the Rubin vase, the Penrose Triangle, and the work of M.C. Escher enough to know when we’re being duped, and usually, we can explain why things may appear to be different than they actually are.
In this case, though, I’m fooled every time. I know that the squares marked A and B are actually the same shade of gray. When I first saw this picture, I checked the colors. I also know that the surrounding colors and the shadow make them appear to be different. But I still think A looks darker.