bad hire doesn't necessarily mean bad/stupid/incompetent person, it just means bad hire. might not be a fit for the role, might not be a fit for the company. for example, i freely admit i was a bad hire at Google because i got demotivated by big corporate/political bullshit getting in my way, it just wasn't for me. then i went to a 20 startup and, in the words of the CEO, "saved the company" and scaled it to 200 people
and no i didn't make up 20%, Gartner did a study on it. and most people with management/hiring experience report the same.