The whole point of the precautions is to reduce the chance of something happening. People have built a PC on carpet without a care in the world and the machine was fine. People recommend these steps because it's a real thing that can happen and it really can cause you to lose money, lose time, and drive you up the wall trying to figure out what part went bad. It's a real danger and the risks are steep.
Being "grounded" is not a universal trait. It's basically grounded relative to something else, most commonly the Earth. You use an ESD bracelet to ground yourself to your metal PC chassis so that the ground between you and your equipment is the same. If there's no (large enough) difference in the electrical charge between you and your...