Why OnComponentBeginOverlap don't work with character's root capsule component?

simply I just started learning UE4 and C++
and I need to using Overlap function so watching this tutorial

https://unrealcpp.com/on-overlap-begin/

at there he makes a new Capsule Component
but I want to use character’s root component, so type like this

GetCapsuleComponent()->OnComponentBeginOverlap.AddDynamic(this,&APP_OvergroundCharacter::OnOverlapBegin);

but this not work, and also alreday he said about it.

I want to know why this not work.

ps. sorry for bad English type :frowning: