Psychology Today - Why We're Nicer to Strangers Than the People We Love Most

CAUTION - The visualization in 1 may be triggering for some.

Why is it we so often find ourselves treating the ones we most love the most shabbily? Contrary to popular wisdom, I don’t think that the answer is that familiarity breeds contempt. After all, it’s not that all the wonderful things we loved about our loved ones when they first entered our lives have gradually become repulsive to us (“I hate that you’re so kind to everyone!”). Rather, it’s that our tolerance for all the things we’ve always disliked invariably diminishes over time.
Add to this the fact that pain commands our attention far more than pleasure and we arrive at the explanation: We have the least tolerance for the negative qualities of those with whom we spend the most time.

Sometimes our loved ones recieve the bad end because we know they will usually forgive us.

We are in pain, therefore we understand what suffering is all about, thus we feel for others with an open heart.

Yet those most close to us do not accept us, they do not open their minds to us. This angers us. We respond.