Most job candidates feel interview questions can be decoded and hacked, letting them respond to those questions with "perfect" answers.

And they're right, especially if you insist on asking opinion-based job interview questions.

(Quick aside: Is there really a perfect answer to a question like, "What do you feel is your biggest weakness?" I think there is: "If that's the kind of question you typically ask, I don't want to work for you.")

Asking opinion-based questions is a complete waste of time. Every candidate comes prepared to answer general questions about teamwork, initiative, interpersonal skills, and leadership.

That's why you should ask interview questions that elicit facts instead of opinions. Why? I can never rely on what you claim you will do, but I can learn a lot from what you have already done.

Where employee behavior and attitude are concerned, the past is a fairly reliable indication of the future.

How do you get to the facts? Ask. Ask an initial question. Then follow up: Dig deeper to fully understand the situation described, determine exactly what the candidate did (and did not do), and find out how things turned out. Follow-up questions don't have to be complicated. "Really?" "Wow... so what did he do?" "What did she say?" "What happened next?" "How did that work out?"

All you have to do is keep the conversation going. At its best, an interview is really just a conversation.

Here are my four favorite behavioral interview questions:

1. "Tell me about the last time a customer or co-worker got mad at you."

Purpose: Evaluate the candidate's interpersonal skills and ability to deal with conflict.

Make sure you find out why the customer or co-worker was mad, what the interviewee did in response, and how the situation turned out both in the short- and long-term.

Warning sign: The interviewee pushes all the blame and responsibility for rectifying the situation on the other person.

Decent sign: The interviewee focuses on how they addressed and fixed the problem, not on who was to blame.

Great sign: The interviewee admits they caused the other person to be upset, took responsibility, and worked to make a bad situation better. Great employees are willing to admit when they are wrong, take responsibility for fixing their mistakes, and learn from experience.

Remember, every mistake is really just training in disguise... as long as the same mistake isn't repeated over and over again, of course.

2. "Tell me about the toughest decision you had to make in the last six months."

Purpose: Evaluate the candidate's reasoning ability, problem solving skills, judgment, and possibly even willingness to take intelligent risks.

Warning sign: No answer. Everyone makes tough decisions, regardless of their position. My daughter works part-time as a server at a local restaurant and makes difficult decisions all the time - like the best way to deal with a regular customer whose behavior constitutes borderline harassment.

Decent sign: Made a difficult analytical or reasoning-based decision. For example, wading through reams of data to determine the best solution to a problem.

Great sign: Made a difficult interpersonal decision, or better yet a difficult data-driven decision that included interpersonal considerations and ramifications.

Making decisions based on data is important, but almost every decision has an impact on people as well. The best candidates naturally weigh all sides of an issue, not just the business or human side exclusively.

3. "Tell me about a time you knew you were right but still had to follow directions or guidelines."

Purpose: Evaluate the candidate's ability to follow, and possibly to lead.

Warning sign: Found a way to circumvent guidelines "... because I know I was right," or followed the rules but allowed their performance to suffer.

Believe it or not, if you ask enough questions some candidates will tell you they were angry or felt stifled and didn't work hard as a result, especially when they think you empathize with their "plight."

Good sign: Did what needed to be done, especially in a time-critical situation, then found an appropriate time and place to raise issues and work to improve the status quo.

Great sign: Not only did what needed to be done, but also stayed motivated and helped motivate others as well.

In a peer setting, an employee who is able to say, "Hey, I'm not sure this makes sense either, but for now let's just do our best and get it done..." is priceless.

In a supervisory setting, good leaders are able to debate and argue behind closed doors and then fully support a decision in public - even if they privately disagree with that decision.

4. "Tell me about the last time your workday ended before you were able to get everything done."

Purpose: Evaluate commitment, ability to prioritize, and ability to communicate effectively.

Warning sign: "I just do what I have to do and get out. I keep telling my boss I can only do so much but he won't listen.... "

Good sign: Stayed a few minutes late to finish a critical task, or prioritized before the end of the workday to ensure critical tasks were completed.

You shouldn't expect heroic efforts every day, but some level of dedication is important.

Great sign: Stayed late and/or prioritized - but most importantly communicated early on that deadlines were in jeopardy. Good employees take care of things. Great employees take care of things and make sure others are aware of potential problems ahead of time just in case proactive decisions may help.

Obviously there are a number of good and great answers to this question. "I stayed until midnight to get it done," can sometimes be a great answer, but doing so night after night indicates there are other organizational or productivity issues the employee should raise. I may sometimes be glad you stayed late, but I will always be glad when you help me spot chronic problems and bottlenecks.

Like with any other question, always evaluate a candidate's answers to this question based on your company's culture and organizational needs.

Few candidates can bluff their way through more than one or two follow-up questions. Turning the interview into a fact-based conversations helps you identify potential disconnects between the candidate's resume and their actual experience, qualifications, and accomplishments.

And you'll have a much better chance of identifying a potentially great employee, because a great employee will almost always shine during a fact-based interview.