This could roughly be saying half of hires are below average, and the distribution is bell shaped (or triangular to a first approximation). For many jobs, below average can be equivalent to bad.

If you have money to spend, or can wait to hire, you can beat the averages. I've hired a fair amount and done well too, but only by refusing to hire anyone if there are not suitable candidates that applied, which can burn a lot of political capital (your boss sees you've spend x time and money and had y applicant and z interviews and you refuse to hire anyone).

Good, cheap, available, pick two.