Anyone who has conducted workplace investigations has come up against “I don’t know” when asking someone WHY they did something.

Frustrating? You bet. And many times, workplace investigations are met with skepticism and a belief that the person is hiding something, not cooperating, or is incompetent in their job.

The problem is, many times the person being investigated really doesn’t know why they did whatever it was they did.

Everyone is susceptible to making errors, including those who are skilled, experienced, and excellent employees.

Depending on the situation, the reasons for their actions are not always apparent – even to them.

So, repeatedly asking them why they did something will only frustrate both them and you. Worse yet, it will likely either put them on the defensive or make them feel incompetent.

Getting past “I don’t know” in workplace investigations

The key to getting past “I don’t know” is to understand the different types of human error and what leads to them.

Understanding human error

There are four primary types of human error. Understanding each of them not only helps when conducting workplace investigations but throughout every part of our lives.


These are attention-based errors.

With these errors, the plan was correct but there was an error during execution. Slips are most common when factors like fatigue, distracting environments, stress and trying to do multiple things at once are present.


Lapses are memory-based errors.

Like slips, with lapses the plan was correct, but something went wrong in the execution of the plan. Also like slips, they are most likely to occur in situations where other factors such as fatigue, stress, and relying on memory are involved.


Mistakes are knowledge-based errors.

With mistakes, the plan is executed as intended, but the plan was incorrect. Mistakes result from a lack of knowledge or not understanding how to apply knowledge.

In the workplace, these tend to happen when there are gaps in training, when training relies on role memorization, and in unfamiliar environments and uncommon or emergency situations.

On the subject of mistakes, did you know that pointing out their own is one surprising habit of the world’s best leaders? Click here to read four others.


Violations are decision-based errors.

With these errors, a decision is made to violate a rule or procedure and the action goes as planned. It is important to remember that the action is planned – not the incident.

The decision is made with the belief that an incident will not occur as a result. These should not be confused with sabotage, which are cases where the violation is made with the intention of an accident occurring.

Human error in action

To help understand the different types of errors, let’s look at an example.

Imagine you are travelling to another city for a meeting and rent a car to get to the meeting location.

Let’s also assume you don’t have GPS and have memorized the directions from the airport.

You are successfully following the directions but get distracted by your favorite song while driving and miss the exit ramp.

Your plan was right as you intended to take the exit but you were distracted and missed it. You find your way back to the exit ramp and are back on track to your meeting.

You have made a slip.

Then, along the way, you realize you forgot which step you’re on. You are supposed to take three lefts and a right but can’t remember how many lefts you have taken and end up only making two left turns before you turn right.

This memory-based error is a lapse.

Again, you find your way back to the route and come upon a traffic circle. They don’t have traffic circles in your small hometown and you don’t know the rules that apply. You incorrectly drive in the outside lane all the way around. In this case, you did not know the proper procedure.

You made a mistake.

Finally, you are almost at your location. You come to an intersection of two one-way streets. You can see the building you are going to is on the corner to the left of you. But the one-way street is for traffic going right.

You look and see that no one is coming and there are no police around. Next, you decide to drive the wrong way down the one-way street for a few meters and enter the parking lot. You know you are violating traffic laws but feel it is safe to do so.

This is a violation.

Human Error Taxonomy

A graphical summary of the Human Error Taxonomy and the four error types:

Now, back to our situation where the person involved doesn’t know, or can’t remember, why they did something.

In the case of mistakes and violations, the individual successfully performs the action that they have planned. This means they will generally know why they did something as their plan went as intended.

If someone truly doesn’t know why they did something, it was likely a slip or lapse.

To understand the contributing factors in these situations during workplace investigations, you can focus your questions on factors relating to things that cause these types of errors.

These include scheduling practices (fatigue), what was going on around the person at the time (distractions), the culture (time pressure), and task requirements related to memory (are their job aids).

These are just a few examples of potential contributors to slips and lapses.

A skilled investigator can effectively ask the interviewee ‘why’ without ever actually asking them the question directly if they understand what type of error they are dealing with.

Outsourcing workplace investigations

The use of a skilled professional investigator who understands error types, particularly in complex incidents or ones where those involved can’t explain their actions, can lead to a better understanding of contributing factors and effective corrective actions.

Contact us at for information on how we can assist you with your investigation needs. And don’t forget to follow us on LinkedIn.

Did you learn a lot from this post about workplace investigations? Here are three more to check out:

Your Organization Received a Sexual Harassment Claim. Now What?
Effective Communication Techniques to Bring Your Workplace Harassment Policy to Life
Effectively Investigating Workplace Bullying and Harassment Hazards and Incidents

This article was originally published in 2017, but has been updated in 2020 just for you!