Being smart is a good thing. But there can be such a thing as being too smart for your own good. I mean, do you believe in the Tooth Fairy? Do you believe in Santa Claus? When you were a toddler going into your tween years you probably did. But do you believe in evil demonic forces in the shape of a clown??
Seeing is believing but sometimes you are not even too sure if you even saw it. I never saw the Tooth Fairy but I did see a dollar bill under my pillow when I was a little girl. Stan Uris from The Loser's Club was too smart for his own good. He accepted reality as we know it. He was the last one to see IT. The rest of The Losers Club saw IT and had no choice but to believe. Stan did not want to believe until he was outnumbered.
Now fast forward 30 years later, do you still believe in The Tooth Fairy, Santa Claus, or evil demonic entities dressed up as clowns???
Denial became his death sentence...
Stan was too smart, but IT was smarter. IT made Stan succumb to his own smartness.