The same is true if a dog makes contact with human skin. He only does that if he means to. He decides how much pressure to apply and for how long. If a dog only bites acceptable things at acceptable times, it can be entertaining or even helpful. A police dog that apprehends a criminal and restrains him by biting and holding onto his arm or leg can save someone's life.
Problems occur when dogs bite the wrong thing at the wrong time.
For dogs to live in human society, they must inhibit and modify their natural inclination to bite in order to become an acceptable member of society. Even dogs that live in the wild with other dogs must learn to do this. One of puppies' earliest lessons includes learning that he can not run up to an adult dog and chomp down on his ear. That adult dog will let him know in no uncertain terms with a growl, a snarl, a lunge and possibly a snap that he can't do that. The adult may even pin the puppy for a moment.