Never Give Up On A Living Being

The fourth precept is never to give up living beings, not even a single one. If we do so, we at once lose the altruistic intention to attain enlightenment for the sake of all living beings. How can we learn never to abandon them? If we know how to transform all adverse circumstances into conditions which help us towards enlightenment, we will never be tempted to abandon anyone.

...Special care is required in our relationships with those who are close to us, those towards whom we feel an instant dislike and those to whom we have been kind and who respond ungratefully. We honor, respect and make offerings to the enlightened ones but neglect and abandon living beings although our attainment of Buddhahood depends as much on them as it does on Buddhas. In the sixth chapter of "Engaging in the Bodhisattva Deeds" Shantideva says:
The qualities of Buddhahood are gained
Through living beings and Victorious Ones alike,
Why then do we respect the Victorious Ones
And not living beings in the same way?

--from Atisha's Lamp for the Path to Enlightenment commentary by Geshe Sonam Rinchen, translated and edited by Ruth Sonam