When it comes to preparing your resume, your 30 second "elevator speech," a LinkedIn Profile, preparing for an interview and, ultimately, pitching yourself to a prospective employer, the vast majority of topics I've covered concerned selling yourself. As I've discussed over and over, these are your opportunities to present yourself in a way that persuades a prospective employer that you are, indeed, the person they've been looking for.
Something that has recently come to my attention, however, has to do with the topic of overselling yourself in the interview. I am not talking about situations where someone blatantly lies about their capabilities (something, by the way, which I strongly recommend against). Claiming to know C# when you have only casually dabbled in it would be an example of that type of fabrication. Rather, I'm talking about making ambitious promises—which, while well intentioned, in reality have a good chance of bouncing back on you if undelivered.
One company we know had a need for business development in a very specific technical space. One of the candidates they were interviewing had plenty of business development experience in several different sectors but not specifically in theirs. He didn't see it as an issue, however. Business development was business development in his mind. So he worked very hard to convince the hiring manager of his capability to transfer his skills and knowledge base to their particular space. Eventually, the hiring manager was sold and decided to bring him on. Unexpectedly to this candidate, coming up to speed on their product line proved far more difficult than he had anticipated, and eventually he was let go for "weak performance."
Another company was doing scientific development in C#. One of the developers interviewing for the role was well versed in that arena but as a C developer. He, too, convinced the hiring manager that it was a small task for him to come up to speed on C#, but after months of frustration on many fronts, both he and his manager decided it was not a good fit and they parted ways.
The biggest problem in both of these cases is that each candidate must now account for the fact that they were only at their new position for a handful of months. They could choose to simply not list the position on their resume, but now they have to account for that period of time.
It is much better to avoid these complications by being honest with yourself about your capabilities and not setting yourself up for these types of failures by overselling yourself in your job interview. Promise to deliver what you know you can and your new job experience should be much more pleasurable.