^Contrariwise if you try the endlessly repeated "...but why?" trick on a sufficiently young child, say age 6 or 7, they (he or she) will realize instinctively you have caught them in a trap (similar to Star Trek's Spock instructing the renegade computer to calculate pi to the infinite decimal place), but be unable to intellectually conceptualize and encapsulate how to crack it and argue their way out.
This will be seen in the child becoming increasingly frustrated at your "...but why?" gambit and resorting to more and more emotional demonstrations of frustration combined with shared amusement at the 'joke', while failing to 'think outside of the box' and put a stop to your silly nonsense.
"Because..." (child)
"...but why?" (you)
"Because..."
"...but why?"
"Because..."
"...but why?"
"Because..."
"...but why?"
They know you're pulling a fast one over on them, but cannot find sufficient justification to shed the unspoken obligation to give a meaningful answer to each new "...but why?" from you.
OTOH, try this on, say, a slightly more intellectually mature child of age 8, 9, or especially 10 on up, and they'll crack the intellectual trap and nail you for it.