The chestnut speech in "O, R-V, I N-V U". Especially if you identify with PJ. And if you keep in mind that Goofy is effectively serving as a Parental Substitute for PJ's own (inadequate) father. What really makes the scene is how profoundly the speech affected PJ, who changed from dismissing the chestnuts to gathering them in large quantities, which even turned out to be a Chekhov's Gun. Then when he does "come out of his shell" in the second movie... it becomes Heartwarming In Hindsight too.
Goofy: Is there something wrong?
PJ (plaintively): Do I look dumb to you?
Goofy: No way, PJ! Here's dumb! (tosses chestnut at PJ's head)
PJ: Ow! (looks at nut) What's this?
Goofy: A chestnut.
Goofy: Not too perty on the outside, huh? It's all spiny and dull-looking.
Goofy: (takes chestnut from PJ and begins shelling it) But come the right time, the shell falls off and walla! Look at it! Ah-hyuck! (inner nut is shown) It's chock-full of good stuff, (cuddles PJ) and handsome too. Ah-hyuck! (touches PJ's nose affectionately) You know what I mean?
PJ (smiling softly): Yeah, I think I do...