What is the role of a casting input?

I’ve been trying to call a variable and/or custom event from one blueprint to another, but I’ve been failing to cast and now I’m not sure (other than why its failing to cast) what the role of the casting input is (i.e. the object that goes into “cast”).

I’ve tried to mimic what is done in the “Memeory Game”; having a custom event in a blueprint that is used in other blueprints via casting

However like I say it fails to cast. I don’t know if this is the problem, but reading the documentation on casting, the purpose of the object (“logic” in my case) going into casting isn’t explained, and in “Memory Game” (also called “logic”) seems to have no role other than as a means to access the casting node.

I’m sure I’m missing somthing fundemental here, so if anyone could explain/point me towards an explanation on casting and the role of the object going into it I would be much obliged. And if anyone can explain why it is failing to cast in my instance, I would be even more grateful.

Have a look at this thread: Help me understand casting - Programming & Scripting - Unreal Engine Forums