For one thing, asking someone what their greatest weakness is, is a totally worthless and pointless question. I am embarrassed for your using it. It stems from the squeeshy-feeling feminine belief that people actually sit around and ASK themselves such inane questions! Further, it presupposes that a person has the self-awareness to honestly ask AND answer such a question to oneself both meaningfully and accurately. Psychologically, if a person really has the self-judgement to fairly ASK such a question, they probably have the capacity as well to have ADDRESSED and ACTED ON the issue long before they met you. A lot of people have no "greatest weakness" (which implies a RANGE of weaknesses!). A really sound person has no significant weaknesses at all, which leaves many good people in a real jam to try to think one up when asked. For an "interviewer" to ask such an idiotic pointless question out of a need to fill interview time and appear "thorough" and think it will actually yield any meaningful data which they can interpret properly, points to the problem people have in interview situations these days where totally unqualified pinholes such as yourself with absolutely no sense of how to really judge and evaluate people has to resort to some grade school level bullshit that probably came out of a book somewhere on "interview techniques."
I wouldn't have had any further questions either. The fact that you ended the interview abruptly based solely on THAT probably showed him your company wasn't worth pursuing. While expecting the candidate to be totally prepared for anything, you showed him you were completely unprepared for many answers. That you took his reply as a deal-breaking negative is astounding. There are a million reasons why a person might say that (whether even true about the person or not) and be a good OR bad thing. Maybe one person who in the past was a slacker told him he was hard to work with because he was highly driven and perfectionistic demanding exceptional standards of himself! Maybe he just said that because lacking any real weaknesses he could really see and admit to for you, he just said it because he thought it sounded self-effacing, very honest, self-perceptive and what he thought you wanted to hear. Maybe that answer came out of the same book the question came from on "How to prepare for an interview." No wonder jackals such as yourself spend so much time looking to fill positions and interviewing people-- -- so few people in HR really have any real skill in doing it effectively. It is just thrust upon them.
And after ALL the trouble the guy had gone to jumping through loops to get that far in your circuitous maze probably for weeks, you didn't even bother to ask.
So in other words, you as an interviewer are so shallow, that you are much less concerned with why the guy gave such a seemingly honest answer than you are that he didn't probably lie and give you a "good" approved, cookie-cutter answer; one carefully planned, picked and thought out in advance to be "just right" for the interview to tell you what you want to hear.
Abject inanity and unfitness. Sounds like your company is the Stepford Wives. Who do you work for, Google? Going for the "perfect fit," eh? Did it ever occur to you that all those other people saw something good in the guy and the problem was you? In an age where Diversity is supposed to the the alter of truth in everything, one thing you can say today about the modern corporation is that they want NO diversity of thinking and ideas! Only cookie-cutter fit ins. Just diversity in the simple, easy things like skin color that gets the Fed off their back. For all you really know, that man might have been the best thing that ever walked through your front door.
And you should stay far, far away from interviewing anyone ever again. I'd love to hear what YOUR greatest weakness is? If you worked for me, not only would I not trust you to "grow" anyone into the well-groomed automaton position of brain-washed group-think you obviously have in mind for whomever you hire to assure they "fit in" properly, but I would probably demote or fire you for releasing a candidate on such thin, specious grounds with absolutely no idea what his answers even meant. If you fuck up such easy things, what more important things must you get wrong every day? I can get an 8th grader at minimum wage to do the "Pavlov's Dog" level of brain-dead interviewing you apparently conduct and I'm sure it would save the company a great deal of money with no worse results.
Case closed. Is it any wonder this country is in sorry shape? You are a fucking idiot drone and the real question is how stupid must a corporation be these days to allow a pinhead as yourself to aspire to the level of being in the position of judging others? That must be your greatest weakness----- the illusion that you know what you are doing. Obviously all you need to get into your company is to do the very worst things-- -- -- give planned, rehearsed, cookie-cutter answers that actually reflect NOTHING of the real person being considered for the hire other than his willingness to CONFORM TO GROUP THINK. The problem with group think is that if it is even a little bit wrong, then, THE ENTIRE GROUP IS WRONG. Of course, being the fact that your company placed you in such authority, obviously I don't expect one watt of this to ever get through and make any sense to you-- -- -- you have been properly "grown" to fit your role as head imbecile.