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. You cannot in the same gesture shake a hand, and give a blow. So there are natural antidotes to emotion that are destructive to our inner well-being.
Matthieu Ricard, Habits of happiness: TED 2004
Humans are very bad at multitasking. This can have a silver lining.