One aspect of loving-kindness is a quality that we take for granted, the quality of feeling grateful. I was in Bodhgaya, the place where the Buddha was enlightened. Now according to the story of what the Buddha did after he became enlightened, one thing was to spend 7 days looking at the Bodhi tree which had given him shade, which had helped him to get enlightened. And he showed his gratitude by standing and gazing at the tree for 7 days.
Do we ever feel grateful for things like a tree, or for something which has helped us? But when we develop this quality of loving-kindness, we learn to appreciate and feel grateful for things, for little things, for small things, which we normally take for granted.
In a way one of the things in meditation, in the spiritual life, is to realise this: to see that we have all these qualities within us, just to see them, just to realise them, and this can make such a difference to our self-perception, it can make such a shift of attitude in us. So in this way, as with rejoicing, we can find so many reasons why we feel grateful.