I think it's impossible to be kinder to others without being kinder to ourselves first. And I think it's all-out impossible to be kind to ourselves when we've lost our sense of magic, of wonder, in the world.
I think it's natural for wonder to go on hiatus, at least in the so-called modern age. I think we've anesthetized ourselves to it by protecting ourselves in a spongy, poisonous layer of cynicism or numbing ourselves so thoroughly, we wouldn't find wonder in if it rode up on a unicorn and started quoting Shakespeare to us.
So, how to remedy that? I don't know. Start small. Tell yourself you're allowed to be happy, that happiness isn't a shirking of responsibility. Tell yourself it's okay to do or say the wrong thing because, man, we try so very hard. And trying that hard is bound to result in a few mistakes and misunderstandings along the way.