When we take a close look at our minds, we can see that the quality of thoughts passing through the mind gives rise to the same qualities in our being; i.e. think angry thoughts, become angry, think kind thoughts, become kindly.
All too often we find ourselves abiding in the former. It's one thing for an angry thought to arise, it's another to entertain it. When we ruminate in such thoughts they build upon one another, snowballing into an uncontrollable emotion that is then communicated through our words and actions.
Net Result = Everyone, First and Foremost Ourselves, Suffers More.
Realizing this, and being committed to the ideal of relieving rather than contributing to the burdens of other beings, it really becomes prudent to set aside time in order to intentionally generate loving and kind thoughts.
Metta meditation is one way of doing so. Like an athlete training in a gym in preparation for an event, setting aside time to concentrate on cultivating thoughts of loving kindness within a supportive environment helps us develop the skills necessary to succeed in the big event...daily life.
Abiding in a mind entrained in loving kindness, we become friendlier to the world, learning to better accept ourselves, others, and the unexpected circumstances that arise along the way.
Thinking loving and kind thoughts, we become loving and kind.