When I helped create telephone switches and datacomm equipment (back when I was young enough not to be considered senile and useless by private industry because I am over 40), many components were redundant: there would be both an A and a B side to the switch. If a power supply failed on the A side, then the B side power supply took over. If the A side incoming fiber card failed, the B side took over. The theory was that if one card failed, it would inform the operator, and the other side would take over. The chances of one of these components both failing before the phone company had a chance to swap out the bad card was quite small.
This is what redundancy gives you: if your equipment is 98% reliable, and you can silently (or nearly silently) switch over to another piece of equipment of similar reliability, and you can get the first failed equipment replaced within a couple of hours, the likelihood of losing service was tiny--fractions of 1%. (Some equipment, such as individual cards responsible for providing service to several subscribers, were usually not redundant. This was a cost tradeoff.)
If you have seen the X-ray of the guy with a spear through his head -- and who managed to remain conscious and talking through the ordeal -- think of this as a reminder that an astonishing amount of your brain is clearly redundant. (Or perhaps, not even used!)