The development of friendliness (mettā), sometimes translated as ‘loving-kindness’, progresses through various stages in much the same way as an evolving friendship gradually deepens.
The practice starts with learning to be more friendly towards those aspects of ourselves to which we are averse or resistant. This doesn’t mean that we have to like them, but at least we can be less negative and more hospitable towards them. Initially this may mean relating to experiences which are unpleasant with an attitude of noncontention or peaceful co-existence.
We can then progress to a more non-reactive receptiveness, and with continued development we can actively befriend the so-called unpleasant experiences, which alters the definitions of what is pleasant and unpleasant — if we are more friendly to disagreeable experiences, they are not so disagreeable anymore.
Judging some personal trait as bad or wrong and then turning it into an object of aversion or rejection is just another conditioned self-activity, albeit sometimes reinforced by society. Similarly to developing a deep friendship, the practice of mettā allows us to be less judgemental of apparent faults and at the same time to come closer to the seemingly unpleasant aspects of ourselves and see them more clearly for what they are — just self-defined tendencies.
Through befriending the negativity in our own minds, we can more naturally respond with friendliness to the negativity we experience in others. With continued practice we can develop an expansive attitude of non-judgemental openness or ‘unconditional love’ towards ourselves and all beings.
This reflection by Ajahn Thiradhammo is from the book, Treasures of the Buddha’s Teachings, (pdf) pp. 121-122.