One advantage of having multiple people do the same job is that unless both are ...

One advantage of having multiple people do the same job is that unless both are dogshit incompetent, you can tell whether your problem is the person doing the job, or the job you're asking them to do.

If you ask a running coach to coach me and then find out that I am slow as a snail, you might conclude that the running coach sucked. But if you hire another one and find the same result then you know I suck.