A person who thinks they know everything is commonly called a know-it-all, but more formal terms include omniscient (all-knowing) or descriptive words like egotist, narcissist, or someone with a superiority complex, often masking insecurity or overcompensating, notes Vocabulary.com, BBC Science Focus Magazine, Merriam-Webster, and BetterHelp.
Most of us know someone who is convinced that they are an expert at everything, regardless of their actual knowledge. You may have heard people like this referred to as "know-it-alls." Many know-it-alls can be challenging to be around, but they may not mean any harm by their behavior.
"Omniscient." Vocabulary.com Dictionary, Vocabulary.com, https://www.vocabulary.com/dictionary/omniscient. Accessed 09 Jan. 2026.
Those with narcissistic tendencies also tend to think they know best--even compared to the most educated people out there and in the face of contradictory scientific evidence.
The Dunning-Kruger effect describes a disturbing cognitive bias that afflicts us all. People with limited expertise in an area tend to overestimate how much they know—and we all have gaps in our expertise.
Some people have such a fragile ego, such brittle self-esteem, such a weak "psychological constitution," that admitting they made a mistake or that they were wrong is fundamentally too threatening for their egos to tolerate.
Lead them to reexamine opinions by asking reflective questions. Avoid what they will perceive as an insult by taking care not to challenge their opinion or recommendation. Instead, acknowledge their expertise, but lead them to rethink what they've said. For example: “What if we changed the deadline?
🤔🚫 Five Questions a Narcissist Can't Answer 🚫🤔 Here are five questions a narcissist simply can't answer: 1️⃣ Anything regarding the truth 🧐 2️⃣ Anything about giving credit to others 🙅♂️ 3️⃣ Anything about failing or losing ❌ 4️⃣ Anything about vulnerability or their true self 🌫️ 5️⃣ Anything about their interactions ...
Another mental health condition, narcissistic personality disorder (NPD), in particular, has an influence on a person's need to always be right. Symptoms of this disorder include: Arrogance or egotistical behaviour. Extremely high sense of self-importance and a desire for high status.
The most overlooked symptom of narcissism is aggressive, habitual non-listening, where they talk excessively and dismiss or interrupt others with phrases like "but..." to regain control, masking deeper issues like fragility and a need for admiration, especially in covert or vulnerable types who often appear charming but are inwardly insecure. It's overlooked because it's subtle, masked by faked interest, and often mistaken for simple rudeness rather than a core disorder driven by a fragile self-image and lack of empathy.
synonyms: know-all. egoist, egotist, swellhead.
Yes, agathokakological is a real, albeit rare, word, an adjective meaning "composed of both good and evil," coined by poet Robert Southey in the 1830s from Greek roots for "good" (agathos) and "bad" (kakos). It's considered a nonce word (a word created for a single occasion) and isn't in common usage, but it's officially recognized by dictionaries like the Merriam-Webster Dictionary and Oxford English Dictionary.
/ləʊˈkweɪʃɪs/ A loquacious person talks a lot, often about stuff that only they think is interesting. You can also call them chatty or gabby, but either way, they're loquacious.
Understanding the Psychology Behind Know-It-All Behavior
Some individuals adopt know-it-all personas to mask feelings of insecurity or compensate for past failures. In certain cases, this behavior may be linked to a superiority complex.
Self-righteousness (also called sanctimony, sententiousness, and holier-than-thou attitudes) is an attitude and belief of moral superiority derived from a person deeming their own beliefs, actions, or affiliations to be of greater virtue than those of the average person.
The Dunning-Kruger effect is a cognitive bias in which people wrongly overestimate their knowledge or ability in a specific area. This tends to occur because a lack of self-awareness prevents them from accurately assessing their own skills.
As a Harvard-trained psychologist, I've found that there are seven phrases you'll hear from highly narcissistic people:
Symptoms
Keep busy with other things. When you get the urge to check your body, distract yourself by going for a walk or calling a friend. You could also try these relaxation techniques: breathing exercises.
The "3 E's of Narcissism" refer to three core traits often seen in individuals with narcissistic tendencies: Empathy impairment, a profound lack of understanding or sharing of others' feelings; Entitlement, a belief they deserve special treatment and admiration; and Exploitation, using others for personal gain without guilt. These characteristics highlight how narcissists often struggle to connect emotionally, feel superior, and manipulate people to meet their own needs.
The following are 16 key phrases to disarm a narcissist:
The number one trait of a narcissist is often considered a grandiose sense of self-importance (grandiosity) combined with a profound lack of empathy, where they see others as tools for their own gain and have an inflated, often unrealistic, view of their own superiority, needing constant admiration without acknowledging others' feelings or needs, as highlighted by HelpGuide.org and The Hart Centre. This core creates other behaviors like entitlement, manipulation, and arrogance, making them believe they deserve special treatment.
10 biggest red flags in a relationship and what to look out for
But it does provide some rough guidelines as to how soon may be too soon to make long-term commitments and how long may be too long to stick with a relationship. Each of the three numbers—three, six, and nine—stands for the month that a different common stage of a relationship tends to end.
Personality disorders involve pervasive patterns of unusual behaviors, thoughts, and emotions, making it hard to function, with common signs including unstable relationships, identity issues, extreme mood swings, impulsive/risky actions (like self-harm or substance misuse), persistent distrust, intense fear of abandonment, difficulty with emotional regulation, problems controlling anger, lack of empathy, and trouble with boundaries or self-image.