If all of your parts are good from the start, I agree. But if you are building a computer for the first time and get just one bad part, it can be difficult to

If all of your parts are good from the start, I agree. But if you are building a computer for the first time and get just one bad part, it can be difficult to isolate where the problem is if you don't have a box full of spare parts you know are good that you can swap out one by one until you find the bad part.