The rule for all of us is perfectly simple. Do not waste time bothering whether you ‘love’ your neighbour; act as if you did. As soon as we do this we find one of the great secrets. When you are behaving as if you loved someone, you will presently come to love him. If you injure someone you dislike, you will find yourself disliking him more. If you do him a good turn, you will find yourself disliking him less. There is, indeed, one exception. If you do him a good turn, not to please God and obey the law of charity, but to show him what a fine forgiving chap you are, and to put him in your debt, and then sit down to wait for his ‘gratitude’, you will probably be disappointed. (People are not fools: they have a very quick eye for anything like showing off, or patronage.) But whenever we do good to another self, just because it is a self, made (like us) by God, and desiring its own happiness as we desire ours, we shall have learned to love it a little more or, at least, to dislike it less.
Mere Christianity, C.S. Lewis