He who receives kindness should never forget it,

but he who performs kindness 

would be wise to forget it.

We should always be grateful for the kindness that others have shown to us. Kindness can relieve our fears and worries, and lessen our suffering. Remembering the kindness of others and how much it meant to us, we will be more inclined to pass it on.

But when we are kind to others, remember it not. Thinking of our kindness to others could allow pride to creep in. We might look down on the person who needed our help—mentally patting that person on her head like we would a child. While we, dwelling on our good actions, mentally pat ourselves on the shoulder. Unaware of the tiny changes within us, we have given pride a home. And there goes our humility.

The Buddha warned us of the four poisons of greed, anger, ignorance, and arrogance. Pride is a slippery slope with the bottom being arrogance. So just as we need to guard against anger arising, we need to also guard against pride.