In our interactions with others, gentleness, kindness, respect are the source of harmony
Peace comes from within. Do not seek it without. It can be argued that peace and happiness comes from the subjective internalised perspective of realizing things could be worse and being grateful they aren't. The alternative view that peace and happiness comes from the objective external perspective of having more and better things than at present, while important for growth, can be a never-ending source of jealousy, dissatisfaction and disappointment. A balance of the two, where people are grateful for what they have while striving for more seems the best blended perspective.
Attachment is the source of all suffering.
The mind is the source of happiness and unhappiness.