Because it learn the features of say a picture and than goes in the details of a picture in a fractal pattern. Like I bet you don't even know how you recognize things, you'd have to think about it. Like a car has wheels etc. But then you recognize cars in 2 milliseconds, wait how did that happen? It's your hardware. Now computers can do this too, they can recognize images. They can see the difference between dog breeds, I can't.