An ancient curiosity

"....we are not half so anxious that our friends should adopt our friendships, as that they should enter into our resentments. We can forgive them thought they seem to be little affected with the favours which we may have received, but lose all patience if they seem indifferent about the injuries which may have been done to us.....They can easily avoid being friends to our friends, but can hardly avoid being enemies to those with whom we are at variance."

This one has always fascinated me. The negative of having positive relationships with our enemies is certainly worthy of our attention, but why is not the positive aspect of our friendships themselves taken as seriously and earnestly? At worst, these represent zero sums, and that we should be able to better armor ourselves against our inevitable social and psychological injuries by strengthening our wonder and joy and gratitude along side strengthening our fortifications against hardships themselves. Is it somehow impossible to advance without defences capable of deflecting all but the most massive bombardments?