You could extend that line of thinking thusly:
The spectator (being smart) does not believe in "magic," so the very claim that something magical is happening - one card changing into another, someone reading your thoughts - would be absurd and lead to embarrassment.
A magic gesture serves to define WHEN the magic is allegedly happening.
Dai Vernon said, "Confusion is not magic."
If the spectator leaves not knowing what happened, we have failed. In the big scheme of things, that includes knowing when it happened and (allegedly) how it happened.
Are you a psychic, a gifted sleight of hand man? Do the cards change on their own? Does the coin vanish or are you just hiding it?
These are the questions one must answer before presenting magic to an audience. Otherwise, you are telling multiple stories that have no connection - or worse, no clear story is told at all.
I would suggest reading WOnder's The Books of Wonder for more on this. He really captured the importance of thinking magic through from this perspective. If you ever have the chance to work with a director, this is how they think. What does the audience see and what does that lead them to conclude? If the audience does not "see" a clear and congruent story, then it is bad theater.
Magic - up close or on the stage - ultimately, is theater. We know the person didn't REALLY die at the end of Les Mis, but we suspend our disbelief and go on a journey which allows to us feel what it would be like if they had. Magic allows us the chance to give that gift of feeling wonder to a person. Wonder produced by performing things that are unreal - but creating a safe place to allow people to suspend that disbelief and "play."
Brad Henderson