This is a beer tap:
When you tap (into) a barrel of beer (=insert a tap into it), you can take some of the beer and drink it, but a much, much larger amount of beer remains in the barrel.
Suppose I want to sell cars, and I decide to make a sexy advertisement that associates cars with sex. My ad "taps into" people's desire for sex--I use that desire to make them buy cars, but I don't decrease the desire for sex. I use some of it, but the total amount remains the same.
People think Bob is smart= Bob is thought of as smart.
Americans like cheese, but many Chinese people think cheese is disgusting. = In america, cheese is thought of as delicious, but in China it is thought of as disgusting.