When you compliment back when someone compliments you, what's the reason?

If you don't do this, what do you think is the main reason people do this?

I've seen this happen many times, and I think I have an idea, but I'd like to hear from you.

That's the courteous thing to do
I owe a compliment back
I want to have sex with this person
It's something I was taught to do
I want to show my romantic interest
It's just a reflex
If I don't compliment, I suck
Select gender and age to cast your vote:
When you compliment back when someone compliments you, what's the reason?
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