I would that SN is not necessarily a weak spot, although it can be. SN is what we already know, what we come into life with. So it is the path of least resistance and not a place in which we will grow; it is the safe place. The NN calls us aspire, to grow into that sign.
So someone's Moon to your SN make incline you to just rest on your laurels, so to speak, and not cultivate and develop the balance that NN-SN is about.