Why must getSlot be invoked on self when used in a method?

Hello

I'm quite confused about the following behaviour:

Example:
Io> m := method(nil)
==> method(
    nil
)
Io> getSlotReturnsNil := method(getSlot("m"))
==> method(
    getSlot("m")
)
Io> getSlotOnSelfReturnsM := method(self getSlot("m"))
==> method(
    self getSlot("m")
)
Io> getSlotReturnsNil
==> nil
Io> getSlotOnSelfReturnsM
==> method(
    nil
)

Why does the invocation of getSlot("m") in getSlotReturnsNil return nil?
Best regards, Eebel