Because it brings an imbalance in the relationship - I am giving them my full attention, and they are not. Now there are situations in which this is okay - for

Because it brings an imbalance in the relationship - I am giving them my full attention, and they are not. Now there are situations in which this is okay - for example in a close relationship where these things are understood, so maybe I have brought along a newspaper to read while waiting for the food to arrive, and my lunch date is checking their email. Contrary to the comment below, the narcissistic person is the one who is texting, not the one who is waiting - because the person who is texting is almost certainly overrating the importance of him sending an immediate reply to his correspondents.