Mr. Dolphus Raymond makes this remark to Scout about Dill in chapter 20. In chapter 19, Dill starts crying during Mr. Gilmer's cross-examination of Tom Robinson. Jem tells Scout to take Dill out of the courtroom. Scout leads Dill under some trees and tries to explain that prosecutors have to act that way. Mr. Dolphus Raymond inserts himself into their conversation and agrees with Dill, saying it makes him sick, too, to hear people talk to blacks with such disrespect. 

Scout believes Mr. Raymond is an evil man because he is known as a drunk and has fathered mixed race children. When Mr. Raymond offers Dill a drink from his bottle within a paper sack, Dill finds out it's only Coca-Cola. Scout scolds Mr. Raymond for "making yourself out badder'n you are already." He explains that he pretends to be a drunk because "it's mighty helpful to folks," that is, it's easier for people to believe he lives among the blacks because he's a drunk than to believe he lives among them because he prefers that way of life.

When Scout asks him why he would share his secret with her and Dill, Mr. Raymond explains he trusts them because as children, they can understand his simpler explanation. Then he says he also decided to tell them his secret because Dill's crying showed that he was still untainted by the perspective of the townspeople. The horrible things Mr. Gilmer said to Tom that made Dill cry will one day, when Dill's older, seem "not quite right" but will no longer provoke him to tears. He will get used to the way whites treat blacks, and it won't bother him anymore. Mr. Raymond's point is that Dill's instinct is correct; what Gilmer said should have moved him to tears and made him sick. But seeing it more and more often as he grows up, things will catch up to his instinct, making him immune to the injustice he sees around him.

This scene takes place in Chapter 20 just after Scout and Dill take a break from the trial of Tom Robinson. Dill has become physically sick from witnessing the prosecutor's cross-examination of Tom. Mr. Gilmer shows Tom no respect, repeatedly referring to him as "boy." So, Scout leads Dill outside for some fresh air. "We chose the fattest live oak and we sat under it." On the other side of the huge tree trunk is Dolphus Raymond, a notoriously "evil man" who lives with the Negroes, has a black mistress and who has fathered several "mixed chillun." Scout and Dill quickly make friends with him, and Mr. Raymond shares a dark secret: He only pretends to be drunk, and his ever-present bottle-in-a-bag is only Coca-Cola--not whiskey. The Coke he shares with Dill settles the boy's stomach, and then the "fascinating" Mr. Raymond shares his racial views with the children. Dill's tears come from a youthful innocence, but he will be tougher and wiser when he "gets a few years on him." It is Dolphus Raymond who tells Dill

"Things haven't caught up with that one's instinct yet. Let him get a little older and he won't get sick and cry.  (Chapter 20)