An overbite combined with protruding lips, mimics the expression of sadness and disappointment. So if someone has this combination, they will be judged to be sad or disappointed more quickly compared to other normal faces. Strong cheekbone with wide jaw mimics the expression of happiness. So if you have this combination, you will be judged as cheerful or approachable even if you are feeling neutral inside or if you dont want to be approached!
The point being your immutable facial features largely determine how you are judged, or even "how people think you are presenting yourself". What people usually see is you expressing mild disappointment not that you just have an overbite. If you are happy you have to "present" yourself to be happy and for that you have to know which cues you have to give out and which cues you have to avoid giving out. Ofcourse if you have a naturally happy looking face you wont have to compensate. But imagine this combination : eye bags + underbite + recessed maxilla + protruding lips + negative carthal tilt, you noticed that people judge you to be angry or sad or some sort of negative emotion even when you are neutral. When you tell them you are not experiencing any negative emotion at all, they will just make fun of your face. To them its amusing that some neutral guy can look that desolated but for you it sows confusion.
This is very similar to "Zero Error". Where 0 of a measuring instrument is slightly shifted thus producing a Correctable Systematic Error. Correcting the error involves offsetting the ruler with a corrective value such that measured 0 reflects true 0.
Paradoxically, being fake like "managing your expressions" is actually being authentic and not managing your expressions is "being fake". To be authentic you have to know your facial predispositions and what these dispositions mean and how to exaggerate or inhibit each of these based on what you are communicating.
To the intelligent mind here i debunk the commonly stated proposition of "Why do you want to be fake? just be yourself" to be a harmful piece of advice.
More scattered thoughts: Here I only describe communicating in a specific channel of communication (facial expressions) There are other channels where same principle applies:
But such judgement and consequent willful ignorance is harmful especially if you are constantly misheard and misjudged (Exactly the type of person that should be practicing "faking", so that the harmful bias of default settings is neutralized). Studing and practicing faking makes it easier for your authentic self to come out.