Your brain quickly recognizes the important elements: a man, a dog, snow and a countryside path. Once the scene makes sense as a whole, you’re less likely to examine whether every individual detail follows the same logic.
The footprints are also less visually interesting than the people and objects in the picture, so your attention is naturally drawn elsewhere.
Only when you compare the man and dog directly does the contradiction become obvious:
Dog walking through snow = paw prints.
Man walking through the same snow = no footprints.Apparel
And once you’ve noticed it, it’s difficult not to see it.