In order to efficiently and effectively know how to tell if someone is lying to you, you must first understand why the target subject would lie to you in the first place.
We all (need to) lie, it’s human nature. It’s necessary and highly useful in this social world we live in.
In most cases our (technical) lies are harmless and are often used for good, these are “white lies”. Then there are “strategic lies”, deceptions with the intent of personal gain, advancement or even pleasure.
Those are the two basic types of lies we can broadly categorize; white and strategic. That gives us the what.
Telling the truth is easy and effortless because we are merely describing a hard encoded memory. Whereas telling a lie takes significantly more effort (regardless if the subject is an expert or even a sociopathic liar).
Generally, a lie begins with the conscious decision to do so. Then using the imagination, new but false information has to be generated. And finally, the mind has to be constantly kept in check to withhold the old but true information.
There’s just so much thought processes compared to speaking the truth. That’s just how deception works.
Deception Indicators // Eye Movements, Facial Ticks, Hand Gestures, Body Language, Vocal Tones, Speech.
[ How to Tell if Someone is Lying to You ]