No applicant is 100% honest and open in an interview. This is not a revolutionary bit of news. But it tells me something if you are incapable of doing enough self-reflection to come up with an answer other than "My weakness is that I'm so awesome, it's a drag."
Because it is the low-hanging fruit of answers. It screams, "I don't want to appear less than perfect to you, so I'll attempt to turn a good quality into a 'weakness'." With true self-reflection, I believe anyone can identify an actual weakness and ways to address it. As I stated before, I interview MS4s for residency, not college students for med school. My expectations may be higher than med school interviewers.
I should also note that I do not frame the question as "What is your biggest weakness?" but rather "What is a weakness that you have had to address over the past few years?" That avoids the whole "My perfection is truly my biggest weakness, if I say it's something else I'm being insincere!" scenario above.
I think it is probably the case that a lot of people use this as a safe answer (a la "my biggest weakness is that I care about other people so much"). However, someone's greatest "weakness" is a subjective experience. It is dependent on their perception of themself, and this perception is developed over a long history of lived experiences, thoughts, and interactions. Being able to appreciate the subtlety and nuance going on inside an applicant's head is difficult. You are not trained psychoanalysts, nor are you psychics. I think interviewers would do well to check themselves before leaping to conclusions about the introspection or lackthereof of applicants.
That said, all of this could be ameliorated by simply asking more direct questions or simply stating a question that gets at the heart of what you really want. I have been a part of very thoughtful interviews where I was asked questions such as "How are you misunderstood?" or "what is a common weakness that you share with others" or "what three words are you unhappy that people use to describe you". Regardless of what's asked, use follow-up questions. It's your show. I've answered the "what is one of your weaknesses" question in a way that my interviewer didn't like ("I don't like to ask for or acknowledge the need for help") and he simply waved his hand at me and told me to come up with another one. That's fine, it was a genuine answer that actually
is one of my greatest weaknesses, but if it's not the kind of discussion he wanted to have, I'm happy to delve further precisely
because I have enough introspection that I'm actually quite aware of many of my shortcomings (and what people perceive my strengths to be, and what my actual strengths are, and what people perceive my weaknesses to be, and what I wish my strengths were, and what I project that my strengths are, and what I've worked hard at but do not actually constitute strengths, and how I compensate for them, and how I can't compensate for them, etc etc).
I think it's easy to assume a lot about interviewees--and I hate the canned answers and have conducted plenty of interviews where I suspected the interviewee was giving me one--but to assume certainty on this is dangerous and unfair to applicants. Ask questions that reveal what you want, use follow ups, and accept that you cannot know as much as you think you know. I think interviews can and should be a fun opportunity to learn.
