Jimmy wakes up on the morning of his 18th birthday and drives to the clinic for his mandatory injection of love serum. This is a special medicine that makes him fall in love with the next person he sees. This is required of all adult citizens, once per year.
It is very unlikely that the person he sees will also have just been injected, and will also fall in love with him. So the world is full of unrequited love–but it is full of love. And everyone understands each other’s pain and sympathize with those in love with them, because they feel it themselves–helplessly, uncontrollably, mandatorily–for someone else.
This world is a bit kinder to each other, a bit more understanding and sympathetic toward each other, a bit more loving for each other. Because everyone, by default, knows what a heartbreak is.