The Illusion of Knowing – highlighting and underlining
Have you ever finished a study session, closed your book full of neatly highlighted passages, and thought, “That was productive—I really learned a lot today”? It feels good. The trouble is that sense of achievement might be an illusion of possessing more knowledge about something than is the reality. Psychologists call this the illusion of knowing (Brown et al,2014).
The illusion of knowing happens when our brain mistakes familiar, visible actions—like highlighting or underlining—for actual learning. These strategies give us the feeling that we are mastering new material, but they confuse familiarity with understanding.
In the modern era, taking photos of slides that the presenter uses could be an illusion of knowing if this is not followed by revision, reflection, and repetition to lay strong neural pathways for future retrieval and use.
Highlighting acts like a comfort blanket. Seeing those bright lines across the page reassures us we’ve “done something.” But learning isn’t about decorating a book—it’s about reshaping how we think, making connections, and using that knowledge in real situations. Another major downside is that the illusion closes our minds to further learning.
A small metaphor from dog-walking
Imagine taking a dog for a walk. Along the way, the dog pauses to “mark” every corner by peeing, every tree, every pole. From the dog’s perspective, this act might seem like it establishes territory ownership. But in reality, it doesn’t make the place theirs—and often, they don’t even remember it the next day. Similarly, a dog might smell a flower today with curiosity and then smell it tomorrow with the same novelty, as if it were the first time.
It’s a charming trait in dogs—living in the moment, experiencing things with fresh eyes (or noses). But as a metaphor for learning, it’s helpful to remember that these acts don’t add to memory or a more profound understanding. Marking territory doesn’t establish ownership, just as highlighting text doesn’t secure knowledge. It’s a visible sign of activity, but not evidence of learning.
And just to be clear—I’m certainly not a dog researcher, nor am I claiming to understand the science behind why dogs do this. This is simply an observation, used as a light-hearted way of explaining how our study habits can sometimes mislead us.
Some effective strategies
Strategies are effective when one develops deep self-awareness of their own knowledge and thinking on any subject (metacognition). To achieve this, instead of relying on highlighting alone, try strategies that strengthen active learning:
Self-testing: Challenge yourself with quizzes without looking at the notes. Struggling to recall information strengthens memory. Using flashcards with key facts to revise information is another way of self-testing and making knowledge concrete.
Explaining aloud: Teach the concept to a friend, or yourself in the mirror. If you can explain it clearly, you probably understand it. My favourite is explaining things to my dog. They seem to be very attentive listeners.
Connecting ideas: Ask, “How does this new piece of information fit into what I already know?”
Spacing and revisiting: Revisiting material after some time helps shift it from short-term memory into long-term understanding. The idea is to actively retrieve things learnt periodically to strengthen neurological circuitry and solidify learning (retrieval practice).
Highlighting and underlining aren’t bad in themselves—they can help mark what’s important. But when we rely on them as the primary tool, we risk falling into the illusion of knowing. Authentic learning requires greater effort, reflection, and practice.
So, next time you reach for the highlighter, remember: the real work of learning begins not on the page, but in your mind. Like a dog happily marking every corner on a walk, highlighting can feel satisfying in the moment—but it doesn’t guarantee ownership of the knowledge.
Resources that inspired the article
Kate Dunning, Kevin Mackie, Alan Charters and Andrew Lockey. Pocket guide to teaching for clinical instructors. 4th ed, John Wiley and Sons Ltd, 2025.
Disclaimer: This blog article represents my opinion on this topic and is not based on rigorous research. For learning strategies, I recommend consulting specialists in teaching and learning.