So basically...
3rd and 7th:
You: "I'm concerned about stuff related to my 3rd function."
Dual: "Well don't be. It doesn't matter as much as you seem to think."
4th and 8th:
Dual: "I took care of stuff related to your 4th function."
You: " Awesome! I'm really glad I don't have to deal with that."
If we get used to being with our dual and then have to make due without him/her, it sucks really bad because once we've experienced not having to worry about our 4th function, we can't go back. We wonder how we ever got by without our duals. (The same applies to our 5th function, except even more so.)