At the beginning, your neural network is a complete pile of junk. It starts with no knowledge – no idea of what is or isn’t a dog. All the dials and knobs are set to random. As a result, the answers it provides are all over the place – it couldn’t accurately recognize an image if its power source depended on it. But with every picture you feed into it, you tweak those knobs and dials. Slowly, you train it.