In 2005, I was deep in grad school. I was the kind of tired that comes from too many late nights, too much bad coffee, and the creeping suspicion that the more you learn, the less you know.

I did a lot of reading outside my assigned school reading and I picked up Marcus Buckingham’s The One Thing You Need to Know. I recognized Marcus from his work with Gallup and I was a big fan of StrengthsFinders at the time.

Marcus argues that we can and should dig for the “one thing” in any given area that serves as the controlling insight. The one thing that gives us the most clarity and understanding on a given problem, area, or relationship. This sounds over-simplified, it may be, but it is a useful lens on issues and areas of gaining mastery.

The theory is that in any domain – great managing, great leading, great individual performance – there is one controlling insight that, if you understand it, makes everything else clearer. One core truth that organizes your thinking.

His key “one things” break down like this:

For great managing, the insight is to discover what is unique about each person and capitalize on it. Buckingham argues that great managers don’t try to fix weaknesses or manufacture sameness. They obsess over what each individual already does exceptionally well and build around that.

For great leading, the insight flips: discover what is universal and focus people’s attention on it. Leaders need to move groups, not individuals, and that requires finding the shared fear, the common aspiration, or the singular challenge worth fighting and making it vivid.

For sustained individual success, the insight is more personal: discover what you don’t like doing and stop doing it. Not just “do what you love,” but specifically identify the activities that drain you and remove them over time, because willpower is finite and you can’t outwork your own energy leaks.

The book draws from Gallup’s enormous employee engagement research, and the writing is sharp.

How to Apply It

The practical application is an exercise in excavation. Buckingham invites you to keep asking “what is the one thing?” in any domain you’re trying to improve, not to oversimplify, but to find the load-bearing wall.

What, if you got this right, would make the other things easier or even unnecessary?

Try it right now with something you’re struggling with. Pick a persistent problem at work and ask: if I had to bet on one root cause or one lever that moves this more than anything else, what would it be? Write it down. Then ask whether your current actions are actually aimed at that thing.

Most of the time, they aren’t. We scatter effort because specificity feels risky. Buckingham’s book is a push toward intellectual courage, the willingness to commit to a diagnosis.

Where the Idea Shines and Where It Gets Complicated

Here’s what I’ve wrestled with over the two decades since reading that book: the “one controlling insight” is a powerful lens, but it’s still just a lens.

Life, organizations, and people are genuinely complex. Most stubborn problems have multiple causes stacked on top of each other (see the series of Systems Theory articles I wrote last year).

A team isn’t struggling because of one thing. It’s usually a combination of unclear roles, a trust deficit, misaligned incentives, and one or two personality clashes. Reducing that to a single insight can sometimes mean you fix the loudest thing and miss the systemic issue underneath it.

There’s also a real human vulnerability here. We want the one magic thing. We want the single supplement, the one conversation, the one restructuring move that cleans up the mess. That desire is so strong that we’ll sometimes convince ourselves we’ve found it and stop looking too soon. The “one thing” framing can accidentally become a permission slip to stop thinking.

And yet the search for it is still enormously valuable.

Think of It Like the 80/20 Rule

The Pareto Principle doesn’t tell you that 80% of your results come from exactly 20% of your efforts in some mathematically perfect way. It tells you that your inputs and outputs are almost certainly not equally distributed, and that the imbalance is bigger than you think. It’s a forcing function for prioritization, not a law of nature.

Buckingham’s “one thing” works the same way. The point isn’t that complexity doesn’t exist. The point is that most of us are so overwhelmed by complexity that we never commit to a primary lever at all. We manage everything at medium intensity and wonder why nothing moves.

Asking “what’s the one thing?” forces you to rank, to commit, to put a stake in the ground and test your bet against reality. Even if the answer turns out to be two things, you’re still miles ahead.

The Takeaway for This Saturday

Pick one area of your professional and/or personal life that feels stuck. Apply Buckingham’s question, not as a final answer, but as a diagnostic tool.

What is the most likely controlling factor here? What does the evidence point toward, even imperfectly?

Then act on that one thing first and adjust as you learn.

The world is complicated. But complicated systems still have leverage points. The skill is in finding them and having the discipline to stay there long enough to see what moves.