When the world has the Way,
running horses are retired to till the fields.
When the world lacks the Way,
warhorses are bred in the countryside.
There is no greater loss than losing the Tao,
no greater curse than covetousness,
no greater tragedy than discontentment;
the worst of faults is wanting more-always.
Contentment alone is enough.
Indeed, the bliss of eternity can be found in your contentment.
Contentment is the secret to happiness and peace. All that you need is to be content with what you have, who you are, what is occurring in the current moment and whom you have in your life. That is it. Nothing else is needed to be happy and to be at peace.
Discontentment is the cause of all suffering. Simply by wanting something or someone to be different or feeling that something is needed in order to feel happiness causes suffering. You suffer until that thing that you think you need is attained or that situation is changed. However, the desire that existed does not become satisfied. Instead, it turns to the next thing that is needed or something else that needs to change. It is never satisfied and suffering continues.
Discontentment is also the reason for mankind’s tendency towards acts of war. Without contentment, there is a constant need for more power. This leads to a desire to rule over others, to conquer and to obtain that which someone else has.
What Lao-Tzu is saying here is that when humankind is content and in tune with the Way, weapons are not needed and available resources (the example of horses is used in the verse) are turned towards the creation and support of life. When humankind is discontent and out of touch with the Way, those resources become used for the conquering and destruction of others.
Imagine a world where all of the resources, time and energy that are used in the preparation and execution of war where instead placed on the betterment and support of life. Imagine if the intelligence that was focused on more advanced and more destructive weapons was instead turned to the eradication of disease.
All that is needed for this to be a reality is contentment. That alone is enough.