Of course there are different degrees of telling the truth. Does your prospective employer need to know that you stole a pencil from a classmate when you were in second grade? Obviously not. Do you need to disclose to a legal employer that you failed the bar exam and will need to take it again? Of course. Your bar status is highly material to your job as an associate.
In an interview, you need to tell the truth about material facts. You also have an obligation not to mislead an interviewer through omission. For example, if it is clear that an interviewer believes that you left your last firm voluntarily, you need to set the record straight if you were actually asked to leave. But you are under no obligation to share all of the sordid details of your demise.
The prospective employer does not need to know that you had a messy affair with the managing partner's secretary. It is sufficient to state that both you and the partners you worked for agreed that the firm was not a good fit. Telling the truth does not require telling all!
Too Much Information Can Unnecessarily Weaken Your Job Prospects.
I was once screening a candidate for a search, and I noticed that she had a big gap on her resume. I asked her what she was doing during this time. She answered, "I was a drug addict." While that seemed to be the truth (and clearly a phase that had long passed in her life), it would have been more effective to tell me that she had taken some time off to deal with personal or family issues.
What if the partner you worked for was unbearable? Try "Smith & Jones was a difficult place to work." Saying that the partner you worked for is a notorious jerk will only raise questions about your ability to be discreet. It will also suggest that you are apt to blame someone else when things go wrong.
What if you received a poor performance review because you were bored out of your mind? Try "Some of the partners I worked with were very impressed with my legal skills. But I did not find residential real estate closings challenging, and I don't think I did my best work for the partners in charge of the residential side of the practice. That is why I want to be at a firm that principally does commercial real estate." In other words, take some responsibility for your demise, but do not feel the need to elaborate at great length.
The "Whole Truth" Can Prevent an Interviewer from Drawing Negative Inferences.
Sometimes the whole truth is best because it provides a good explanation for something that might be perceived as a negative. It also removes any speculation that you have some skeletons in your closet (e.g., the gap in your resume is there because your mother was sick and you left work to care for her).
I often joke with candidates that in the absence of contrary information, employers will presume that you were institutionalized during any breaks on your resume. But in general, the rule is that you need to tell the truth and nothing but the truth; but you do not need to tell the "whole" truth, as long as you do not mislead.
Are You Planning to Relocate to Boston Permanently?
Where you intend to live long term provides a good illustration. What if your significant other is in her third year of medical school in Boston? If she lands a residency in California, in all likelihood, you will want to make a lateral move to California in order to be with her. But it is also possible that she will end up doing her residency right in Boston. Furthermore, you would eventually like to return to Texas, where your family lives.
Do you need to disclose this to potential legal employers in Boston? I would submit that you do not. As long as you have a meaningful chance of staying in Boston, your future employer does not need to know the "whole truth" (i.e., that you would consider remaining in Boston for the long term but there are a lot of unknowns).
What if you like employment litigation but are not crazy about employment counseling? If you are applying to a firm that mainly does litigation but expects you to do some counseling, it is okay to say, "I really enjoy employment litigation, and I'm happy to also spend a portion of my time doing counseling." As long as the job would have a litigation focus, no one needs to know that in a perfect world, you might avoid non-litigation work. That's the "truth" and "nothing but the truth."
It is impossible to address every issue that might arise in an interview setting. But that underscores why it is so critical to prepare for interviews. Learn what you can in advance about the firm, department, and interviewing attorneys, but also take the time to think about the questions that you might be asked. If you take the time before an interview to think this through, you will have much greater success in being truthful. At the same time, you will come across as a straight shooter without providing information that you will later wish you had withheld.