But if you’re wondering why the adults can’t remember Pennywise and how IT tormented them, you're not going to get a solid answer: that’s where the fan theories come in. In the novel, Stephen King never really fully elaborates on the why behind it all, which has led many to speculate on their own as to why the memories are gone. And honestly, Reddit users will do a much better explaining it than I ever could, as one redditor, YouArePostHuman writes , the kids “simply forgot. Part of the hold that IT has on Derry lies in it’s [sic] ability to sort of make people ignorant of what’s going on, and that includes making people forget all of the atrocities that IT commits. In the novel, Mike never forgets because he never leaves, and when he calls all the Losers to tell them that IT is back, they all slowly start to regain their memories.”