Mind training is based on the idea that two opposite mental factors cannot happen at the same time. You could go from love to hate. But you cannot, at the same time — toward the same object, the same person — want to harm and want to do good.

Love looks not with the eyes, but with the mind, And therefore is wing’d Cupid painted blind.

Ah me! love can not be cured by herbs.

Love is the silent saying and saying of a single name.

And now good morrow to our waking souls,
Which watch not one another out of fear;
For love, all love of other sights controls,
And makes one little room, an everywhere.
Let sea-discoverers to new worlds have gone,
Let maps to other, worlds on worlds have shown,
Let us possess one world, each hath one, and is one.